Miracast sending support for the Linux Desktop

Describes the status as of 2018-05-15, things will have changed considerably since then.

Current approach:
 * Python userspace program that just streams a test image
 * Program speaks directly with wpa_supplicant through dbus (bypassing NetworkManager)
 * Program tries to become group owner

Caveats:
 * Firewall may need to be adjusted for DHCP server
 * Does not properly reset state when killing (destruction of P2P Group)
 * Does not react to P2P group creation
 * Cannot start the DHCP server (or client) because of this
 * No support for audio streaming so far