Refactoring: plugins should not leak into the core

If you pollute core with plugins stuff, then you have
to update both the core and the plugin(s). We really should consider the
core with extension point so that it is easier to add behavior for other
plugins.

OCP rulez!

The Full Text Search system events are now run as 'app' instead of 'root'

Change-Id: Ic5d76ff4bb795a05aa522a9f1b1a5db7b6fd26a6
Merge commit 'refs/changes/17/3117/8' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  Refactoring: plugins should not leak into the core

Change-Id: Ice41b2ddcc8ffd546bee392ba936769c27df1f98
This is Tuleap 7.5.99.71

Change-Id: Ia03b1f5dd8f30458fe9ba3dd374c00fcb2358860