Implemented QmitkXnatEditorUpdateSession() to realize the server url update
and and the corresponding for QmitkXnatTreeBrowserView.
Some little changes to the Editor UI.
Merge remote-tracking branch 'origin/bug-17959-UpdatingServerUrlDoesNotAffectUI' into bug-17959-UpdatingServerUrlDoesNotAffectUINEU

Conflicts:
	Plugins/org.mitk.gui.qt.xnat/src/internal/QmitkXnatEditor.cpp
	Plugins/org.mitk.gui.qt.xnat/src/internal/QmitkXnatTreeBrowserView.cpp
Changes in Ui-Interactions.

Added warnings that there are no session parameters (if there are none).

Cleaned up the code.
Changed revision_tag and md5 sum.
Merge branch 'bug-17959-UpdatingServerUrlDoesNotAffectUINEU'