For #88: Provide a PHP script to combine not-up-to-date translations

This is for #88. Look in the comments of that issue to get a screenshot and a live demo.
It is a PHP script that combines the translations (for example fr.json, de.json) with the root file if they are incomplete.
So for example, if there is an entry "Sprint 33" in en.json, but not in de.json, it will use the data from en.json instead (but only for that version, the others are translated!).

It prevents such fails like adobe/brackets#5092 (or also #90), too. We could also add more translations as they needn't be maintained that well.

In this PR, there are also some changes that are needed to get this to work, such as changing the buildNumbers in de.json to match en.json.

Let me know if you have further suggestions.