:bug: Fix (all?) first render and resize issues

-Use observeItem instead of deprecated $activeItem, observeItem is called a bit later apparently
-Force full render on pane change, this fixes a few issues:
 - incorrect update when the buffer has changed outside the editor
 - minimap not updated when syntax theme has changed
Get a handle to dispose observer
Move 'with-minimap' class to constructor
Replace fullyTokenized by tokenized event
:bug: Fix scroller update on line-height change
Avoid sending minimap:updated on scroll
:bug: Full update is necessary on scroll-view resize
:bug: Recomputing minimap size is also necessary

The bug was visible when the dev console reduced the window and minimap needed to have a scroller.
Merge pull request #115 from jrouviere/canvas_rendering

Fix some render and resize bugs