Autostart an app at start-up

[torwag]

To mimic just the standard behaviour some people might like to start xochitl right from starting the tablet. Oxide would still be there, returning with a long keypress but you would end up in the xochitl man window directly after start. That might be usefull if you use the rM 99% of the time for note-taking and would like to avoid the additional click during start-up. It might also speed up the process from cold start --> note-taking.
That implies that it works well together with #15

[Eeems]

Blocked by #40

[Eeems]

I've tweaked the API for applications to take this into account: https://gist.github.com/Eeems/728d4ec836b156d880ce521ab50e5d40#file-03-apps-md

[Eeems]

Working on implementing this as part of the apps api.

[Eeems]

486cefe just implemented the ability to automatically start background applications. The Apps API has the concept of a startup application, but right now that has to be a launcher of some sort to work properly. That said, I'll update oxide to also include code to handle launching a configured startup application and that should solve this.

[Eeems]

Done.