Make filenames in the local repo object browser direct-download links
for repo types that expose a downloadable file route (rpm now).
- add downloadableTypes capability map keyed by package_type
- render file names as <a href download> when the type is downloadable
- fetch the repo package_type on the Objects page as the modularity hook
- enable rpm via the yum files route /api/v2/remotes/<repo>/files/<path>