Add git hash and branch to version_git field in API

[oscgonfer]

Currently we only provide a tag overview of the git version of the API (with \n included...): "1.1.5\n"

Would be good to get a version more descriptive, aligned to that provided by the firmware, for instance: 0.9.8-8ecac5c-dev (hardware info, sam_ver field: https://api.smartcitizen.me/v0/devices/16733). This would be:

tag-reducedhash-branch

I guess something simple, not priority at all.