Debian support

[peakwinter]

• Replace assorted references to Arch-specific directories and utilities.
• Users and groups: http -> www-data
• Replace netctl with networkd or similar, see Network management via networkd #5
• Replace python-pacman with python-apt driver
• Verify Python version compatibility (features should work on at least 3.4 and up!)

See the following resources for tips.

• python-apt integration in applications.py: https://github.com/GetSkylark/core/blob/master/skylark/applications.py
• Image building and deployment: https://github.com/GetSkylark/scripts/blob/master/build.sh