Add translate_sync to grunt

This allows us to specify new translations once
in `en.json` and running `grunt translate_sync`
will sync translations to other language files.
Merge pull request #201 from WorldBank-Transport/feature/add-translate-sync

Add translate_sync to grunt
Add Vietnamese translations
Merge pull request #203 from WorldBank-Transport/feature/vietnamese-translations

Add Vietnamese translations
Add Chinese translations
Merge pull request #204 from WorldBank-Transport/feature/chinese-translations

Add Chinese translations
Add indicator calculation button
Add English strings for Scenario tab.
Cleanup based on PR feedback
Merge pull request #202 from WorldBank-Transport/feature/calculate-button

Add indicator calculation button
Fix Chinese translations

The translator put them in the msgid instead of the msgstr, so I just
copy-pasted. I tried to match up the line numbers as best I could so
that hopefully everything ended up in the right spot.
Merge pull request #206 from WorldBank-Transport/feature/fix-chinese-i18n

Fix Chinese translations
Merge pull request #205 from WorldBank-Transport/feature/scenarios-translations

Add English strings for Scenario tab.
Refactor GTFSFeed to use status field
Update django translation strings