Split plugin

These commits add a buffer to Gerrit calls in the facade (d4062b6) and split the almighty GerritDecorator class into 3 independent classes (b4b56a6 and f7c8567), namely GerritInitializer, GerritDecorator and GerritPostJob. Each of them to their own business.  
Version is bumped to 2.1.0-SNAPSHOT