i18nliner-handlebars (part II)

extraction and runtime for ember handlebars

test plan:
1. verify string extraction:
   1. `rake js:generate i18n:generate` before and after this commit
   2. confirm `config/locales/generated/en.yml` is identical, except the
      now you get a bunch of new ember strings
2. verify js translation file generation:
   1. `rake i18n:generate_js` before and after this commit
   2. confirm the files in public/javascripts/translations are identical,
      plus a whole bunch of new ones for ember
3. confirm you can now use i18nliner-y features:
   1. block helper with no key `{{#t}}hello world{{/t}}`
   2. inline helper with no key `{{t "hello world"}}`

Change-Id: I7bca8aeba462e68f27973fa801e7f7dbc7b3c9ef
Reviewed-on: https://gerrit.instructure.com/43158
Reviewed-by: Jennifer Stern <jstern@instructure.com>
Product-Review: Jennifer Stern <jstern@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>