Branding with Localization

Closes #27 (closed), which is about LW branding not being applied anymore if you use a language other than English.

The way to fix this is to use the Firefox locales and programmatically change all occurrences of "Firefox" to "LibreWolf". There are two approaches to the problem:

1. We ship all those locales directly with the browser

This is the way that Waterfox does it I think. It is also what this MR does. Disadvantages would be a longer build time for both the source tarball and the actual build (a few minutes each), as well as larger LW binaries (I have no idea how much larger).

2. We generate language packs

With a simple mach command you could also use my existing code and generate language packs (in the form of a .xpi extension). Here is a working example language pack for German I built. Those could then either be manually installed, or automatically downloaded when the user selects a language (the second one is how Firefox does it). Disadvantages: Would be a bit harder to set up. Advantages: Could be split up from the main build process, so the language packs could be built in a separate repository and don't have to be updated that much.

@stanzabird @fxbrit what do you think? I think having language packs automatically be installed would be the cleanest solution.