Blockly bundle locales

This PR dramatically reduces the amount of time to build our Blockly-based JavaScript apps.

Before (only building English and pseudolocalized locales):
```
$ time grunt rebuild
[...]
Done, without errors.

real	0m37.081s
```
After (building ALL locales):
```
$ time grunt rebuild
[...]
Done, without errors.

real	0m15.949s
```
It also reduces the payload size of the final files:
Before:
```
196218 /en_us/bounce.min.js
160441 /en_us/calc.min.js
227974 /en_us/eval.min.js
193261 /en_us/flappy.min.js
154157 /en_us/jigsaw.min.js
278952 /en_us/maze.min.js
341921 /en_us/studio.min.js
274640 /en_us/turtle.min.js
167866 /en_us/webapp.min.js
```
After:
```
 48375 /bounce.min.js
 12458 /calc.min.js
203850 /common.min.js
 18625 /eval.min.js
 45315 /flappy.min.js
 13356 /jigsaw.min.js
132228 /maze.min.js
117503 /studio.min.js
128540 /turtle.min.js
 25735 /webapp.min.js
```

The only tradeoff is that we now load four `script` tags in our `_blockly.html.haml` view partial, instead of one, to grab the proper localized strings from for the app-specific and the common bundles:
```haml
  %script{src: "#{blockly_path}js/common#{pretty ? '' : '.min'}.js"}
  %script{src: "#{blockly_path}js/#{js_locale}/common_locale.js"}
  %script{src: "#{blockly_path}js/#{js_locale}/#{app}_locale.js"}
  %script{src: "#{blockly_path}js/#{app}#{pretty ? '' : '.min'}.js"}
```

(edit: Separating out the dev-mode scripts stuff into a separate pull request.)
This provided an acceptable solution to a very frustrating problem for those of us actively developing with Blockly. It sounds like you've since set up an alternative solution to this issue that you prefer, so this fix can be removed.