Changes related to Phil's changes to interstitials and feedback:
- Switched Turtle to use new interstitials and feedback.
- Moved common messages to common.soy.
- Generated en_us files.
- Loosened duplicate message checking in xliff_to_json.py.
Merge remote-tracking branch 'codedotorg/mooc' into mooc

Conflicts:
	i18n/common.pyc
	static/maze/generated/en_us.js
	static/turtle/generated/en_us.js
	static/turtle/template.soy
Regenerated files after merge.
Fixed change preventing application-specific errors.
Added msg tags for interstitial messages in Turtle.
Made all of the Turtle feedback work with the new system, with the
exception of a bug displaying feedback after Level 9 of Turtle 3.
Fixed post-interstitial bug and cleaned up code.
Merge remote-tracking branch 'codedotorg/mooc' into mooc

Conflicts:
	static/common.js
	static/extracted_msgs.xlf
	static/maze/generated/en_us.js
	static/maze/maze.js
	static/maze/template.soy
Fixed poor merge.
Merge remote-tracking branch 'codedotorg/mooc' into mooc

Conflicts:
	i18n/xliff_to_json.py
Added the show feedback function in karel/maze.js, and also merged the new template.soy in Maze to Karel. Passed the i18n test, but the rendering of the html is broken.
Hided the blocks in the maze.html in Karel by loading the common.css.
Changed the Maze.reset function to BlocklyApps.rest, so that the resetButtonClick function in common.js can be correctly called.
Added the readonly.html for generating hint messages.
Removed the foo message in template.soy of Maze and Karel.
Corrected the feedback mechanism by changing result to Maze.result in karel/maze.js. Also added the numBlocksNeeded field in karel/template.soy.
Moved properties such as Maze.LEVEL to BlocklyApps.LEVEL, so that functions in common.js would work correctly.
Added required blocks for Karel 1. Questions: The params field in the required blocks are no longer supported. Is this intentional? If so, need to update the required blocks defined. Needs to implement a test that does block A or B for required blocks.
Minor formatting for common.js. Did not change code.
Small tweak to feedback iframe resizing.