Adding Version url with version number and git sha

Added validation of version file
Refactor to have version in binary
Change to git sha
Change to git sha
Change back to git commit
Added copyright
Enable legacy download counts.

Those values are stored in the extra-info for the entity.
This is basically a hack, and will be removed soon.
Merge pull request #246 from fabricematrat/version-file

Adding Version url with version number and git sha

QA:
make server, go to http://localhost:8080/v4/debug/info
Check that version and id are unknown and that you get a log saying that the version file is not found

Add a version.yaml in cm/charmd/ with version: something and id: something 
Check again it is displayed and no log are appearing.
Merge pull request #251 from frankban/meta-stats-extra-info

Enable legacy download counts.

Those values are stored in the extra-info for the entity.
This is basically a hack, and will be removed soon.
Sort search results by download count.

Search results can be sorted by download
counts using sort=[-]downloads.