[INTERNAL] cleaned up EditorPool

Pulled methods from EditorAPI into the EditorPool. Changed
LOG statements. Removed unused methods. Completed TODOs and
removed the ISarosSession parameters as the checks are already done
in the EditorManager before the methods are called.

Change-Id: I9508ac4fe24aa28525f6fc00b0dd80e740502aa2
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1828
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>