Begin Dashboard UI layout overhaul

- Layout Canvas and Commit Explorer in Dashboard (Main UI)
  - Screenshot: http://i.imgur.com/Jy3Widx.png
- Remove references to old UI from main.py, including test_func()
- Comment out the call to GGraphicsScene.render_scene() in main.py
  - This call is causing errors (see Issue #6) that prevent the UI from
    loading, so need to remove for testing