When creating a new taks with e.g. createTask(type: Compile, ...) the convention mapping should be automatically set.

Reason:

• normally the standard settings of the convention object will be used with just minor variations, like including only some sources or directories. In this case we would have one line less to write (and the line is not obvious and quite ugly!)
• even if all properties are set within the task, having the convention object defined by default does not matter
• if someone wants to use another convention mapping he can still set it - maybe in a nicer way? Like "conventionMapping 'COMPILE'"?