Translation implementation/process for extensions

[chrisgarrity]

New extension proposal:

How are translations passed

What is the tool chain to generate resources for Transifex/get translations for build.

[towerofnix]

Looks like this was accidentally closed by the merge/06-28 (the commit that "fixes" this was targeting an issue in google/blockly, not the issue with the same ID in LLK/scratch-blocks.)