minor fixes i helicopter.tex, and the plots

eq (9) had a sign error, and the poles was also off slightly. The plots
had "measured" and "theoretical" labeled wrong.
updated plots again
Merge branch 'master' of https://github.com/c-math/QuaRCopter

Conflicts:
	helicopter.pdf
	pgfs/part2_pitch_poles.png
	pgfs/part2_step_pitch.pgf
	pgfs/part2_step_travel.pgf
	pgfs/part2_travel_poles.png
	source/part2/eigen_test.m
	source/part2/part2.m