Facemap is awesome! a few thoughts re dev

#### Issue details
_FaceMap is awesome but increase flexibility to improve flight planning_

Facemap is sooo coool! VERY helpful for me to plan oblique missions with a crewed aircraft - closest I found to actually getting me flight lines that would work - BUT:
*maximum angle is too low (45°) - ideally up to something much more oblique, say 70°
*max number of steps is low - would be nice to increase by 10x
*max elevation is too low, would be nice to increase by 10x
*max step height is too low, would be nice to increase by 10x

With those settings I can simulate a slope and calculate locations for flight lines. Would be even better if you could add groups of faces of different slopes.

Also stepping from all sides is weird, when I'm trying to plan mapping a canyon wall - I have to extend the polygon bounds way outside of the canyon so I can ignore those parts. Not sure how you could make it only go from one side of the poly though.

#### Version
_1.3.77 build 1.3.8110.38294 Windoze_

#### Platform
[X] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

#### Airframe type
_NA_

#### Hardware type
_NA_

#### Logs
_None_

The issue names no files, tests, or entry points. Start by locating the Facemap implementation and clarifying which requests are in scope; completion is not defined because the limits, grouped faces, and one-sided stepping behavior all need decisions.

Written by the indexing model from the issue text.