Store the location a package can be found at, and display this on the package
page.
If available, link off to the git repository containing the package.
I'm thinking about adding more fields to this table, and the sha1_hash values
will make this tricker.
Therefore, remove the value, and adjust the existing code to cope. This commit
also adds a new test which coveres some of the changed functionality.
Add some new pages /branches and /branch/... as well as a new git_branches
table. Also extend the email processing to enter the branch information in to
the database.
Rather than just storing the URL in the guix_revisions and
load_new_guix_revision_jobs tables. This will help when storing more
information like tags and branches in the future.
