MechJeb plugin enhancements.

Added Ascent Guidance and Landing Guidance to the page handler.
Added PREDICTEDLANDINGERROR to MechJebRPMVariables.
Added Plot Hohmann Transfer, Landing Guidance, Force Roll, and Enable Landing Prediction to the buttons.
Merge remote-tracking branch 'upstream/master'
Merge pull request #62 from MOARdV/master

MechJebRPM new features