Patch Set 7: I would prefer that you didn't submit this

This changeset
* converts to the 2 pane horizonal view
* removes modified overlay and just uses the > indicator
* renamed StagedNode to StagingEntry
* fixes the naming on the UI objects
* correctly shows partially staged decorations

Open issues from previous comments
* implement a job (general performance/UI threading issues too?)
* implement exception handling (not sure on the correct approach for eclipse plugins)