CAS-1398: Added contributing.md file
CAS-1398: Added contributing.md file

Also modified travis build to check for commit messages based on guidelines

mduszyk/cas,vbonamy/cas,NicolasMarcotte/cas,joansmith/cas,creamer/cas,zhangwei5095/jasig-cas-server,zion64/cas-private,Kuohong/cas,PetrGasparik/cas,lijihuai/cas,fogbeam/fogbeam_cas,moghaddam/cas,battags/cas,daniel-he/cas,fatherican/cas,zhaorui1/cas,fengbaicanhe/cas,fengbaicanhe/cas,icereval/cas,vbonamy/cas,zawn/cas,luneo7/cas,luneo7/cas,fatherican/cas,thomasdarimont/cas,rallportctr/cas,icanfly/cas,zhoffice/cas,daniel-he/cas,zhangjianTFTC/cas,zawn/cas,dfish3r/cas-x509-crl-ldaptive,icereval/cas,DICE-UNC/cas,youjava/cas,fatherican/cas,austgl/cas,yisiqi/cas,fogbeam/fogbeam_cas,fengbaicanhe/cas,thomasdarimont/cas,joansmith/cas,PetrGasparik/cas,thomasdarimont/cas,zhoffice/cas,fannyfinal/cas,nestle1998/cas,rallportctr/cas,Kevin2030/cas,jacklotusho/cas,j-fuentes/cas,zawn/cas,zion64/cas-private,mabes/cas,icanfly/cas,Kevin2030/cas,seanrbaker/cas,Kevin2030/cas,dfish3r/cas-x509-crl-ldaptive,Kuohong/cas,mabes/cas,NicolasMarcotte/cas,creamer/cas,icanfly/cas,eBaoTech/cas,zhangwei5095/jasig-cas-server,zhangjianTFTC/cas,yisiqi/cas,zhoffice/cas,austgl/cas,battags/cas,lijihuai/cas,nestle1998/cas,jacklotusho/cas,thomasdarimont/cas,Kevin2030/cas,moghaddam/cas,NicolasMarcotte/cas,mduszyk/cas,openedbox/cas,j-fuentes/cas,Kuohong/cas,ssmyka/cas,joansmith/cas,battags/cas,seanrbaker/cas,j-fuentes/cas,vbonamy/cas,nader93k/cas,zion64/cas-private,rallportctr/cas,openedbox/cas,yisiqi/cas,j-fuentes/cas,nader93k/cas,zhaorui1/cas,zhaorui1/cas,fannyfinal/cas,nader93k/cas,eBaoTech/cas,austgl/cas,mduszyk/cas,zhangwei5095/jasig-cas-server,rallportctr/cas,DICE-UNC/cas,daniel-he/cas,openedbox/cas,HuangWeiWei1919/cas,dfish3r/cas-x509-crl-ldaptive,seanrbaker/cas,DICE-UNC/cas,jacklotusho/cas,mabes/cas,seanrbaker/cas,icereval/cas,lijihuai/cas,yisiqi/cas,creamer/cas,dfish3r/cas-x509-crl-ldaptive,battags/cas,moghaddam/cas,icereval/cas,ssmyka/cas,zhaorui1/cas,openedbox/cas,PetrGasparik/cas,austgl/cas,jasonchw/cas,zawn/cas,PetrGasparik/cas,jasonchw/cas,HuangWeiWei1919/cas,HuangWeiWei1919/cas,jacklotusho/cas,keshvari/cas,nestle1998/cas,kalatestimine/cas,nestle1998/cas,DICE-UNC/cas,fannyfinal/cas,fatherican/cas,jasonchw/cas,joansmith/cas,zhangjianTFTC/cas,mabes/cas,moghaddam/cas,NicolasMarcotte/cas,luneo7/cas,eBaoTech/cas,fannyfinal/cas,kalatestimine/cas,fengbaicanhe/cas,youjava/cas,Kuohong/cas,keshvari/cas,zhangwei5095/jasig-cas-server,HuangWeiWei1919/cas,luneo7/cas,keshvari/cas,fogbeam/fogbeam_cas,lijihuai/cas,eBaoTech/cas,zhoffice/cas,youjava/cas,ssmyka/cas,keshvari/cas,zhangjianTFTC/cas,youjava/cas,ssmyka/cas,nader93k/cas,icanfly/cas,kalatestimine/cas,daniel-he/cas,kalatestimine/cas,mduszyk/cas,vbonamy/cas,creamer/cas,jasonchw/cas,fogbeam/fogbeam_cas