WIP: Adding Alt Frames (ie. Terrain) to API#460

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billbonney wants to merge 6 commits intodronekit:developfrom

billbonney:mavlink-frame-wip

Commits on Oct 29, 2016

Add Frame to LatLongAlt for Terrain Following
billbonney
committed

Commits on Oct 30, 2016

Update Mission Editor, Guided etc to keep Frame as set
billbonney
committed

Commits on Nov 3, 2016

Refactor accessor to asInt() to be more succinct
billbonney
committed

Commits on Nov 5, 2016

Commits on Nov 6, 2016

LatLongAlt: Update to return true when changed.
billbonney
committed