support multi backend, osm backend and xdg compliance
- Adds support for multiple installer backend [MSM, OSM] which can be defined by a config file, by default will use "MSM" with no xdg support.
- Adds support for OpenVoiceOS OSM installer and separate install code paths
- Adds support for installing, checking if skills are installed, and skill updates from XDG compliant locations for Mycroft/OVOS core
Backend Configuration Example to use OSM:
Configuration Filename: msibackendrc
[Backend]
selectedBackend=osm
xdgSupported=true