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.)
If you'd prefer launching the blockly dev server be routed through the new Rake scripts instead of this Bash script, this can be updated. We need to keep in mind that development-mode Blockly server (which runs a watching process for incremental builds, and also provides an node.JS express server on port 9000) will need to run the `dev` task as opposed to the `build` task, so we will need to add an extra option for this.