Switched the build process to use Polymer UI

The deployed Polymerized output loads, but looks very garbled, and some functionality isn't accessible because of that (non-system dialogs are outside the window, for example).
Moved spark_polymer_ui.* to the top level dir

This resolves 3 problems with the deployed code (`grind deploy`) at once:
1) Fixes the bad output paths for the Open File and New File buttons (relative original paths were resolved to be under lib/polymer_ui).
2) Eliminates the necessity to include widget.dart as a file path, not 'package:...', in spark_polymer_ui.dart (this doesn't fix the original bug #500, however).
3) Eliminates the "../../" prefix in all widget package imports in spark_polymer_ui.html, and correspondingly the necessity to massage this file in grind.dart during deployment.
Bump the app's version due to swithover to the Polymer UI
Addressed review comments + reverted some overlooked wrong changes
Addressed review comments #2
Addressed review comments #3
Merge branch 'upstream/master'
Fixed some missing outputs in deployed code
Replaced 'compile' with 'deploy' in all build sequences

This finalizes replacing non-Polymer with Polymer in the build toolchain. For example, 'archive' now creates a zip of the deployed Polymer UI.
Merge pull request #553 from ussuri/polymer-switchover

Polymer switchover