Feature/load otp data

Ansible roles are normally supposed to rely on their `files` directories; so perhaps the dependency could be reversed: put the gtfs files in `{{ files-dir }}/gtfs` and then place a symlink to that directory at the root of the project hierarchy for human access.

I think another issue here is that the Ansible role relies on the existence of specific files which are .gitignored so their existence isn't guaranteed. I don't know if this is possible within Ansible, but perhaps this could be changed so that it loops over whatever is in `{{ files-dir }}/gtfs`?