Change UIText.java so that "Find Broken Externalized Strings" works

Change UIText.java so that "Find Broken Externalized Strings" works

The current implementation of UIText.java has the bundle name
inlined. Unfortunately, this results in the "Source->Find Broken Externalized
String" workbench action to not find any unused or otherwise inconsistent
keys (an info dialog is displayed saying "No NLS properties files found...".
This fix does not actually fix inconsistencies in the externalized Strings, just
enables the tool to find such inconsistencies (there are currently 42 unused keys
in the UIText.java).

Bug: 309552 (not completed, just as preparation)

Change-Id: I59d831cf1bce49cdc4043232277ec1c862fbce02
Signed-off-by: Mathias Kinzler <mathias.kinzler@sap.com>