Removing all SLUGS autopilot-specific code.
SLUGS has maintained their patches out-of-tree for a long while now.
These will eventually get merged back in, but it'll be easier to evaluate them as fresh commits instead of modifications to this old & dead code, so we'll delete this for now.
Removing old file containing dev notes.
Merge branch 'master' of https://github.com/mavlink/qgroundcontrol into del_slugs
Merge pull request #768 from Susurrus/del_slugs

Delete outdated and unused (all) SLUGS-autopilot-specific code