KSP Interstellar - 0.0.6

This pre-release adds a mission using the nuclear thermal turbojet engines (basically building a long-flight plane), fixes the altitudes for the magnetometer mission to cover the optimum range for each of the bodies scanned and fixes a few bugs in various places.

Since there doesn't seem to be much viable use for the plasma thrusters when first unlocked, I'll skip those for a mission for now and the next mission set will cover whatever I unlock next.