Rewrite olivaw

Olivaw's positronic brain was designed for O3a, and in O3b we need it to be able to do a lot of new things, and do the old things better. It needs a rewrite.

Todo

• Tests
• Add repository manipulation

This is necessary to allow the bot to checkout repositories in potentially arbitrary

• Add DAG processing

Right now the YAML specification can be used to specify a DAG of all the productions, and the Event class processes these into a graph, but olivaw will need to actually handle the process of starting and monitoring each job.

• Add interaction with gitlab and mattermost
• Ensure successful running on (/triggering by) gitlab CI runners