21-serviceworker

This adds the service worker and has been tested before. I left the merge out previously to handle installation of the service worker better. But right now I need this to be merged as all the installation will be handled in the Nomad project and I will make it work there.

Added requirement for aiofiles in order to serve static files from NORTH api, needs to be double checked if it is really needed.

Closes #21 (closed)

requested review from @sanbrock

@sanbrock Please note that this branch is already merged in !27 (merged). I needed this to continue work on other stuff. So if you like we can just merge it from that request and close this without a merge.

LGTM

closed