Convert Languages to CMI

[jenlampton]

Languages need to save settings into a config file.

For reference, here is the parallel issue from drupal.org

[quicksketch]

I'm going to tackle this one next. Language and Locale settings contain our very last variables in the entire system, so in theory after this is complete we'll be 100% variable-free (some double-checking will be required).

[quicksketch]

This is coming along well. Some of our previous variable rearrangement was in the wrong place, causing some confusion. I've converted everything except for locale_translation_plurals, which I'm not sure if it's config or state at this point.

The work-in-progress is at https://github.com/quicksketch/backdrop/compare/175/language_config. We should be able to finish this up this week.

[quicksketch]

It looks like locale_translation_plurals is state, as it is set during string translation (currently still stored in the database). Since it only gets updated on database-driven data manipulation, that means it's stored in the database as well as state.

I encountered some more odd architecture while doing this conversion. It looks like when multiple language types (interface, content, URL) were introduced, Drupal started using the variable table as a sort of cache. This became apparent when converting to configuration that a bunch of the values we were saving weren't "config" at all. I've rewritten the way some functions retrieve these values, pulling directly from modules instead of managing the state of things in variables. This results in fewer things stored in configuration, and it treats configuration as what it should be. Unfortunately it also means that modules that provide language types or language negotiation handlers must be include in the early bootstrap. Considering in almost all situations this is going to be locale.module, language.module, and perhaps entity_translation.module (if we port/include that at some point) I don't think this is a blocker on the implementation.

Tests should be fully passing at this point. We have just one variable left in all of Backdrop, mail_system, which we have issue for at #416.