Implement `/maximize` command.
Implement `/maximize` command.

Issues like #269 highlight that some people just
assume "it should work".
So I have picked the most common resolution (currently)
and set it to it.
http://gs.statcounter.com/#resolution-ww-monthly-201307-201312

Will update if those stats change at some point.
detro/ghostdriver,acarpe/ghostdriver,HelioGuilherme66/ghostdriver,amikey/ghostdriver,yuanzhen/ghostdriver,Lochlan/ghostdriver,acarpe/ghostdriver,xsyntrex/ghostdriver,treejames/ghostdriver,jesg/ghostdriver,jesg/ghostdriver,antoinereyt/ghostdriver,detro/ghostdriver,Vitallium/ghostdriver,xsyntrex/ghostdriver,yuanzhen/ghostdriver,asolntsev/ghostdriver,kuahyeow/ghostdriver,detro/ghostdriver,jesg/ghostdriver,51ttw/ghostdriver,stevenliuit/ghostdriver,HelioGuilherme66/ghostdriver,Vitallium/ghostdriver,asolntsev/ghostdriver,stevenliuit/ghostdriver,treejames/ghostdriver,amikey/ghostdriver,Lochlan/ghostdriver,jesg/ghostdriver,antoinereyt/ghostdriver,51ttw/ghostdriver,kuahyeow/ghostdriver,HelioGuilherme66/ghostdriver