fix for https://bugs.eclipse.org/bugs/show_bug.cgi?id=419108
Bug 419446 - Rap: Session needs to be invalidated if subject changes

https://bugs.eclipse.org/bugs/show_bug.cgi?id=419446
Mobile: Horizontal lines missing

https://bugs.eclipse.org/bugs/show_bug.cgi?id=419861
Mobile: Horizontal lines missing

https://bugs.eclipse.org/bugs/show_bug.cgi?id=419861
in case of an empty tree nothing has to be selected