Add git-annex integration for adventures/music-files

[jkrenzer]

To use git-annex, RPG-Ambience would just need to save all adventures and music files to a folder inside an active git-annex repo. Sync would be triggered automatically, but in an advanced stage RPG-Ambience could use the git-annex-webapp to control the repo or to let the user set all the options for replication.

[JakobKallin]

I'm not familiar with Git Annex, and I likely won't have time to implement support for it in RPG Ambience. That being said, I would appreciate some more info on how it works, so that I can decide what it would involve.

More specifically:

• Is Git Annex something that you would run locally on your computer, or are you referring to a setup with remote repos?
• Does Git Annex have file IDs that never change even when files are moved or renamed? (This is one of the reasons why I implemented Google Drive support and not Dropbox support, as changing the path to a file within Dropbox would unlink it from its adventure without custom change detection logic.)
• Does Git Annex expose its functionality via HTTP? This would be necessary in order for RPG Ambience to access it.

My first idea is that this would be easiest to implement as a script (run on your computer, not inside RPG Ambience) that simply copies your adventures between Google Drive and Git Annex, since this would not require any changes to RPG Ambience. This would probably be the fastest way to get the feature if you're willing to implement it yourself, but it will depend on some of the points above, and it might not be the type of feature that you're interested in to begin with.