[INTERNAL] moved document listeners

Moved the document listeners from the EditorManager to
EditorPool class.

Change-Id: I1587deb3afafce021fc56ba642e722bf303e357e
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1851
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>