[FIX] editors should now properly registered

I do not know the reason to throw

1. an exception if something could not be hooked although this would not
harm the logic flow

2. no even catching those execption and handle them

The EditorListener will no longer throw an exception when it could not
install the required listeners to generate selection events and so it is
no longer possible to screw up the state of the current EditorManager
logic.

Change-Id: I2731f537f15c94a10bc326119087da1c46e3ec40
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1213
Tested-by: Jenkins CI
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>