Improve the handling of Piwik Mobile translations

[sgiehl]

Current behavior:

We have a script that is used to pull specific keys from a defined Piwik instance to update the translation files.

Suggested behavior:

Instead of pulling the translations from Piwik we create an independent translation file for Piwik Mobile, including it's own keys.
That file will be set up on Transifex as an own resource. As the english defaults will be the same as for the keys used before, all other languages will be auto filled by Transifex's Translation Memory.

What would need to be done:

• create a new default translation file for Piwik Mobile in a format Transifex is able to read
• create / change the update script to fetch the translations from transifex instead of a piwik instance
• update all Piwik Mobile files to use the keys defined in the (new) default file
• set up transifex resource for Piwik Mobile
• recreate / update the Piwik Mobile translation files using the new update script (after TM has auto filled)
• remove no longer require "Mobile_"-translation keys from Piwik

[tsteur]

As long as it works and as long as automatically the same wordings/translations are used for certain terms (I reckon that's what this Translation Memory does) I'm 👍