Spaceplane launch

[ElWanderer]

To include:

1. Takeoff
2. Turn to correct bearing for an inclined launch
3. Climb under jets
4. Trigger mode change/rockets when velocity stops increasing
5. Raise apoapsis out of atmosphere
6. Circularise

I have a test script that does all bar 2 (if we ignore turning, all we have to do is change our pitch!) However, it has tons of room for improvements.

Other improvements would include detecting when we are unable to break the sound barrier or descending towards terrain/the ocean.