Use optional constraints for HD default.
Use optional constraints for HD default.

If HD is not explicitly specified, make the track constraints optional
instead of mandatory, so that we work with non-HD cameras.
Fix bug where the video= URL param no longer worked.

aadebuger/docker-apprtc,mvenkatesh431/samples,jjrasche/cell-based-RC-control,fippo/webrtc,dengshaodong/docker-apprtc,jessetane/testrtc,harme199497/adapter,webrtc/testrtc,MahmoudFouad/samples,TribeMedia/testrtc,smbale/samples,jarl-alejandro/apprtc,Edward-Shawn/samples,fitraditya/samples,Roarz/samples,samdutton/apprtc,JiYou/apprtc,mvenkatesh431/samples,TribeMedia/samples,volkanh/volkanh.github.io,samdutton/apprtc,juberti/samples,guoweis/webrtc,smadhusu/AppRTC,bpyoung92/apprtc,Edward-Shawn/samples,virajs/testrtc,ralic/testrtc,ralic/testrtc,overtakermtg/samples,webrtc/adapter,samdutton/apprtc,Acidburn0zzz/adapter,virajs/samples,harme199497/adapter,aadebuger/docker-apprtc,fetterov/samples,82488059/apprtc,jarl-alejandro/apprtc,TribeMedia/testrtc,procandi/samples,TribeMedia/apprtc,webrtc/samples,martin7890/samples,dengshaodong/docker-apprtc,taylor-b/samples,YouthAndra/apprtc,dengshaodong/docker-apprtc,todotobe1/apprtc,Roarz/samples,dengshaodong/docker-apprtc,todotobe1/samples,mvenkatesh431/apprtc,YouthAndra/apprtc,arnauorriols/apprtc,jarl-alejandro/apprtc,samdutton/apprtc,oliverhuangchao/samples,calebboyd/adapter,Acidburn0zzz/adapter,webrtc/apprtc,TribeMedia/testrtc,bpyoung92/apprtc,volkanh/volkanh.github.io,fippo/apprtc,smayoorans/samples,arnauorriols/apprtc,mvenkatesh431/samples,jiayliu/apprtc,todotobe1/apprtc,jjrasche/cell-based-RC-control,smadhusu/AppRTC,bbandaru/samples,tsruban/samples,Zauberstuhl/adapter,xdumaine/adapter,virajs/testrtc,knightsofaa/webrtc,jjrasche/cell-based-RC-control,calebboyd/adapter,mulyoved/samples,myself659/samples,martin7890/samples,taylor-b/samples,virajs/samples,fippo/apprtc,virajs/apprtc,harme199497/adapter,akashrchoksi/newone,leehz/samples,calebboyd/adapter,shelsonjava/apprtc,webrtc/testrtc,pquochoang/samples,oliverhuangchao/samples,samdutton/apprtc,jiayliu/apprtc,mvenkatesh431/apprtc,virajs/testrtc,Zauberstuhl/adapter,webrtc/apprtc,jiayliu/apprtc,smadhusu/AppRTC,rajsek/webrtc,fetterov/samples,smadhusu/AppRTC,EmreAkkoyun/sample,TheKnarf/apprtc,diddie06/webrtc,samdutton/webrtc,shines/adapter,dushmis/webrtc,Temasys/Google-WebRTC-Samples,virajs/apprtc,procandi/samples,procandi/apprtc,xdumaine/adapter,mvenkatesh431/apprtc,shines/adapter,pquochoang/samples,jiayliu/apprtc,shelsonjava/samples,guoweis/webrtc,jessetane/testrtc,YouthAndra/apprtc,jiayliu/apprtc,TribeMedia/apprtc,dajise/samples,Roarz/samples,bemasc/samples,webrtc/apprtc,4lejandrito/adapter,TheKnarf/apprtc,TribeMedia/apprtc,fippo/apprtc,TribeMedia/apprtc,shaohung001/samples,smayoorans/samples,jessetane/testrtc,xdumaine/samples,Temasys/Google-WebRTC-Samples,shelsonjava/samples,TheKnarf/apprtc,akashrchoksi/newone,kosmosby/Google-WebRTC-Samples,4lejandrito/adapter,pquochoang/samples,shelsonjava/apprtc,82488059/apprtc,procandi/samples,arnauorriols/apprtc,TribeMedia/testrtc,virajs/testrtc,b-cuts/samples,leehz/samples,jan-ivar/samples,TheKnarf/apprtc,aadebuger/docker-apprtc,webrtc/samples,jarl-alejandro/apprtc,dajise/samples,bbandaru/samples,jessetane/testrtc,kod3r/samples,shines/adapter,fippo/apprtc,tsruban/samples,sarandogou/webrtc,jan-ivar/adapter,shelsonjava/apprtc,akashrchoksi/newone,MahmoudFouad/samples,shelsonjava/testrtc,arnauorriols/apprtc,overtakermtg/samples,knightsofaa/webrtc,todotobe1/apprtc,todotobe1/samples,overtakermtg/samples,shelsonjava/testrtc,volkanh/volkanh.github.io,shelsonjava/apprtc,mvenkatesh431/apprtc,diddie06/webrtc,Zauberstuhl/adapter,xdumaine/samples,fippo/webrtc,aadebuger/docker-apprtc,fitraditya/samples,shaohung001/samples,aadebuger/docker-apprtc,YouthAndra/apprtc,virajs/samples,arnauorriols/apprtc,virajs/apprtc,smayoorans/samples,JiYou/apprtc,JiYou/apprtc,virajs/apprtc,smbale/samples,tsruban/samples,shelsonjava/apprtc,fetterov/samples,bemasc/samples,samdutton/webrtc,myself659/samples,todotobe1/samples,smbale/samples,mvenkatesh431/apprtc,ralic/samples,dushmis/webrtc,MahmoudFouad/samples,ralic/testrtc,jjrasche/cell-based-RC-control,virajs/apprtc,bpyoung92/apprtc,shelsonjava/testrtc,TheKnarf/apprtc,bpyoung92/apprtc,Acidburn0zzz/adapter,82488059/apprtc,procandi/apprtc,keshwans/samples,webrtc/apprtc,webrtc/apprtc,ralic/testrtc,b-cuts/samples,askdaddy/samples,mauricionr/samples,mauricionr/samples,bpyoung92/apprtc,myself659/samples,shelsonjava/samples,juberti/samples,mulyoved/samples,todotobe1/apprtc,TribeMedia/samples,smadhusu/AppRTC,JiYou/apprtc,martin7890/samples,procandi/apprtc,kod3r/samples,ralic/samples,leehz/samples,YouthAndra/apprtc,procandi/apprtc,kod3r/samples,Edward-Shawn/samples,procandi/apprtc,b-cuts/samples,JiYou/apprtc,guoweis/webrtc,mulyoved/samples,askdaddy/samples,TribeMedia/apprtc,dajise/samples,mauricionr/samples,EmreAkkoyun/sample,ralic/samples,keshwans/samples,82488059/apprtc,jan-ivar/samples,fippo/apprtc,webrtc/adapter,dengshaodong/docker-apprtc,xdumaine/samples,oliverhuangchao/samples,4lejandrito/adapter,bemasc/samples,shelsonjava/testrtc,bbandaru/samples,TribeMedia/samples,fitraditya/samples,todotobe1/apprtc,jarl-alejandro/apprtc,82488059/apprtc,EmreAkkoyun/sample,jan-ivar/adapter