Emit 'position' and 'contextChange' events correctly

Emit position events after model transaction updates.

Emit contextChange events even when staging.

Focusable/ResizeableNode:
* No need to listen to model transact as that now triggers
  a position event on the view

Context:
* Don't listen to 'select' in the base class, just contextChange
  by default.
* Don't close inspector on contextChange if we have a selected
  node that hasn't changed now that they are emitted while staging.

DesktopContext:
* Connect model select and view position events to onPosition.

As a result of fixing context events, debounce the updateDimensions
handler.

Change-Id: I98e0559a993620f057e6036bfd8f6a21bf59e788
Merge "Emit 'position' and 'contextChange' events correctly"