Django migration: #47 (closed).
This MR re-adds Git storage (of extracted source packages).
The implementation has been split into two classes: GitStorage, a higher level class that perform installation, diffs and removal of stored version (removal and diff to be implemented at a later time) and GitBackendDulwich that takes care of implementation details of the git storage using the dulwich module.
The corresponding commit ref is now stored in PackageUpload allowing diffing at some point.
Note: getOlderFileContent and getOlderCommits have been removed as having diff of upload should suffice.
Tests, docs and translation updated.