Added the branch alias for master and changed requirements

This will allow using the dev version to match range requirements when using the dev stability.
I decided to use 1.2.x as dev version for master because the requirement for amqplib has been bumped since 1.1.3

I also change the FrameworkBundle requirement as symfony is now keeping BC. It will be friendlier for people using cutting edge symfony (it makes it compatible with symfony master for instance)