Run full refresh periodically as a background task

I have chosen [clockwork](https://github.com/tomykaira/clockwork) which has nice DSL and could be easily adapted to work with any task runner.

This also needs [shoreman](https://github.com/statianzo/dokku-shoreman) as we have an additional process in the Procfile.
@jirutka [this.](https://github.com/cvut/sirius/blob/master/.editorconfig) You do know that it is called `insert_final_newline`, not `remove_additional_newlines`, right?