Allow reloading configuration at runtime

[Drakulix]

Allow configuration reloading.

This will require to store the configuration parameters somewhere global or linked to their respective Outputs.

[kerscher]

There's also the issue of retaining window positions and all state upon restart.
This haskell library might be a good inspiration for implementation :)

[Drakulix]

Thanks for those suggestions, but I don't think I will support a full in-place restart. This was way easier to do with X11, where the server was separate from the window manager and the window manager could restart without breaking the X11 connections of the client.
I will just offer reloading the configuration and enable loading new backgrounds, keybindings, etc. The current windows and their positions will most likely not be touched.