SimpleRSPicker box size now in A, not on-screen pixels

Also changed SimpleParticleViewer to the same.
StackExtractor2 rejects particles near mask

StackExtractor2 now has a variable maskRadiusA which sets the maximum
distance (in angstroms) a particle center must have from the nearest
masked (i.e. bad) region of the micrograph.  The program also includes
a new display that shows the box locations and which boxes are rejected.