CX Registry: Enable all supported languages by default

Modifies config.defaults.js so all languages for which we have Apertium
MT or Dictd dictionaries are enabled by default.

Externalizes and updates the Apertium language code mappings in the file
mappings.js

Fixes some minor issues with DictRegistry.json.

Change-Id: I727b77b98d8413dc80e4783ae0b3767193bcad85
Merge "CX Registry: Enable all supported languages by default"