Rudder plugins

As the number of plugins increase, we want to normalize their structure and the quantity of information that is duplicated in each of them.

The main points are:

- use a "master" build.conf for rudder-branch and perhaps other properties common to all plugin on a given branch,
- perhaps use a master pom to centralize common behaviour (at least, the maximun number of them)
- perhaps find a simpler to check for license build. We would like to have that provided as a service to all plugin without any code on their side for the status checking (it's extremelly error prone and verbose right now)

Some change will need to be made in 4.1, other in 4.3 (because they will also need changes in Rudder plugin API). This ticket takes care of 4.1 branch.