@TEMP testing
Setup focus and key handler for tree view
@TEMP tracing key handler
Revert "@TEMP tracing key handler"

This reverts commit b8a1cf19a2f87605e26cde5bbedef6aab820ba0a.
Split functionality from __SelectedChanged into __RowClicked in ListView, TreeView, FileController and included in delegates.  This is for keyboard support
Clarified documentation.  Fixed issue with return in files_controller
Added key handlers (empty)
Implemented up, down, left (collapse) and right (expand).  Implemented ____KeyDown handlers in listView and TreeView
Cleaned up non-showing rows after collapse and ignore non-showing rows during operations
Removed testing code
Added TODOs
Merge branch 'master' of https://github.com/dart-lang/spark into cursor

Conflicts:
	ide/app/lib/ui/widgets/listview_delegate.dart
	ide/app/lib/ui/widgets/treeview.dart
	ide/app/lib/ui/widgets/treeview_delegate.dart
Fixed missing bracket
Reorganized treeViewSelectedChanged and treeViewRowClicked to separate responsibilities.
removed unnecessary focus code.  Added Todos.  Clamped selection in _setSelection
added check in setExpanded code.  Reindented
Merge pull request #463 from dart-lang/cursor

Add cursor handling for the treeview (up, down, left, right).  Also, separate selection from clicking functionality.