Add git commit UI.

Also switch to syncfs for git projects.
Added minimap to editor and move scrollbar 20px to left.  Added minimap css to spark_polymer_ui.html
Merge branch 'master' of https://github.com/dart-lang/spark into minimap-create
Add git checkout UI and fix bugs.
Put markers into minimap
Moved minimap generation into ace.dart.  Made _minimapElement getter more intelligent.  Moved numberOfLines varaible outside loop.  Moved minimap css out of code.  Added Todo for background.  invoking setMarkers() as soon as editor starts up.  Removed border on minimap
Cleaned up
Added missing method to mock
Added code folding todo
toolbar changes
toolbar and spark button
Changed minimap-marker css class to have subclass error
Added warning subclass
styled marker for and minimap to be narrower and spaced 1px on the left and right per Devon
made recreateMinimap private and removed from test
add an abstraction layer for SCM support
add a FocusManager class, to track the current file the user has selected in the app
updates from review
Run 'pub get' if not able to find packages
refactor the editor and editormanager classes