Add pitch hold/wings level mode to SAS

[Jason_25]

The SAS is already upgraded in some ways so I think this would be a nice addition too.

Pitch hold would actually hold the pitch you are currently at rather than choosing an arbitrary pitch somewhere between where you are at and the prograde direction like it does now.  For small ships it already works like a pitch hold.  For large ships it does not.

Having wings level bugs me because I want maximum lift during ascent.  Also asking the SAS to level the wings now always results in a pitch down partly relating to the lack of a pitch hold.  At least change the SAS to not make pitch motions when rolling.

[sir_frost]

this is a feature i would like, controlling planes with fine maneuvers is hard, and the SAS system in its current form is not the best autopilot.
we would need some sort of autopilot with a target altitude and target heading. and it would keep level flight on its own.