WIP: Added option to save files in archive

[MrCyjaneK]

This should close #485, which I've opened a couple of months ago.

Usage is simple, just add:

archive:
 - test.txt
 - file2.txt

to your .abstruse.yml and files will be saved in ~/data/archive/{job id}.

Currently there is no way to serve the files with the api (code is written, it just doesn't work, probably an issue with chi?).

TODO:

• Save files on server
• Provide a simple ui for browsing the archived files
• Redirect from /archive/{repo name}/{branch/pull request id} to /archive/{job id}

[MrCyjaneK]

I need extra help with this line - it doesn't work in a way in which I'd expect it to work... I get a 404 instead of the response from function, when requesting /archive/{id}/file.txt