Recover: Re-introduce version control support

[jleclanche]

cc @julen @iafan @ta2-1

So we want VCS support available out of the box. We discussed it wouldn't be in pootle "core", but it should be available as a pootle app.

I have moved what can immediately be moved to pootle.apps.versioncontrol on master. What now remains on master is as follows:

• TranslationProject.scan_files() has a vcs_sync argument which seems completely out of place
• TranslationProject.update_against_templates() contains some versioncontrol logic, adding files if self.scan_files(vcs_sync=False) has new files (?)
• TranslationProject.update_file is tightly bound to vcs, but is also only called from pootle_translationproject.views.vcs_update so go figure.
• pootle_translationproject.views has a bunch of VCS actions, those are pretty inconsequential

So I'd like to do an actual pass together on what is actually still relevant in all that, how can we clean it up, and how can we move it out of where it currently is. I also need to know what the EN requirements regarding the code is (since you don't use pootle's vcs integration - could it be improved so EN can use it as well, or does it just need to stay out of the way?). Whatever remains afterwards will land in the core branch.

Specification

[iafan]

VCS integration is already a part of our broader continuous localization setup, where Pootle is used as a translation front end. Our VCS integration is more flexible, because it is not tied to Pootle projects, and we sync not the .po files stored in Pootle, but the final localized files in various formats as generated by our system. So we are not going to ever use VCS support built into Pootle.

[julen]

My general feeling is you want to build on top of 2afdccacf, which is the cleaned up version that already exists in the core branch.

[phlax]

pootle_fs has recovered this functionality, altho its still somewhat unstable