Import templates from source tree

Launchpad should be able to discover and import translation templates in source repositories hosted or mirrored in Launchpad. Checking in an update to a template in bzr would automatically trigger an import.

We may sometimes have to bypass auto-approval for these templates. For example, when a template is moved or renamed, we should try to spot that and mimic the change in the POTemplate. That could be difficult for repositories mirrored from CVS, or other revision control systems that "fake" renaming by deleting one file and creating another.