prefer radians over degrees

GLM is moving to use radians only.  In 0.9.5 degrees were deprecated and support for them will be removed in 0.9.6.  Since we moved to 0.9.5 we've been getting a lot of warnings about using degrees.  Meanwhile, radians are the natural choice for measuring angles and we should use them in most places except where degrees actually make sense.  Hence this project...

We're now setting -DGLM_FORCE_RADIANS to eliminate the GLM warnings.  We've switched to use radians almost everywhere.  The exceptions are:

(1) Head, Body, and Eye euler angles are still stored (and transmitted over the wire!) in degrees.

(2) We have some hard-coded tuning parameters for the euler angle limits or dynamics of the Head, Body, and Eye -- most of these parameters are still in degrees.

(3) Camera FieldOfView parameters are always stored in degrees.

(4) The JavaScript Quat API still uses degrees, but we'll probably change that soon.

(5) There is a bit of degree magic in the starfield generator and renderer.  I tried to overhaul that code but got something wrong and couldn't figure out how to fix it.  I rolled all of those files back and will try again... someday.

(6) glRotate*() takes degrees, so this is one of the few places where we always have to convert radians to degrees.