Reworked, cleaned up and fixed some splitter problems (not manifested in Spark's case)

1) #draggable still wrong when splitter size > 1
2) splitter position doesn't get restored on startup
Fix: splitter's #draggable was not set correctly for splitter's size > 1
Add attributes for min/max target size to spark-splitter & spark-split-view
Force initial target size to be within specified min/maxTargetSize
Fix: saved splitter position was read correctly but not propagated to splitter
Undo inadvertent change
SHow deleted files in commit dialog.
Merge pull request #1962 from ussuri/fix-spark-splitter

Fix spark-splitter
Merge pull request #1963 from dart-lang/git_delete

SHow deleted files in commit dialog.
Merge remote-tracking branch 'upstream/master' into move-menu-back-to-spark_polymer_ui

Conflicts:
	ide/app/spark_polymer_ui.dart