Eclipse style display texts for Variables view.

Borrowed code from JDIModelPresentation.java to make the variable
display texts similar to how Eclipse shows it.

Note: Needs some cleanup and will end up getting rid off some
presentation logic as we don't need that level of sophistication. It
only makes the code hard to read and also increases the rendering time.
UI enhancements to debug status view.

* Nicer folding: Took the node expanded/collapsed symbol from NERDTree.
  Changed fold text to follow similar style as NERDTree. It still uses
  VIM folding though.