DRM backend + Session interface + EGL
Created by: ascent12
This adds the initial support for running on DRM. It also does a lot of the other related stuff such as opening a session with D-Bus, monitoring devices with Udev, and creating a rendering context with GBM/EGL.
This adds a hard dependency on systemd, as logind and sd-bus is being used for the session. This might not be something that some people like, but it can be made optional if/when an alternate way of handling sessions is implemented, like weston and wlc (optionally) uses.