``RoutePartitionerTokeniserTest`` can now be run headless-ly

* Renamed ``Util`` to ``EditorUI`` because ``defaultLineSeparator`` requires
  loading some UI class, and that is a problem because our CI server can only
  build headless-ly.

* Created ``Editor`` and ``Util.getEditorDocument`` on it.

* ``RoutePartitionTokeniser`` uses now the Eclipse `Document`
instead of raw text. The huge advantage is that there is no longer a need
for handling the line separator, as the `Document` class already contains
the logic for doing this properly.

The test failure was introduced in SHA: 6b796dbde3547b0bf445aa19a30b37998c74d16d