improve class definitions in base.py to work with sim functions

add vSampConvolve attr to Detector class

make vSampShape a property of Detector class with only a getter, since
it depends (uniquely) on vSampConfig and we want it determined on the
fly.

add PSF class to hold atmosFWHM (also start toward adding complexity
for #18)

replace atmosFWHM in Observable class with PSF instance

assign vSampPA attr to detector instance within Observable

add convOpt to Model class (pixel, galsim, or None). not sure where
else to hold this.

remove old Galaxy, Observation, and Model classes, which were replaced
in a previous commit
update sim functions to handle new classes in base.py

in getSamplePos:
    remove fibShape since it is now defined as a property
        of the Detector class

in defineEllipse:
    replace model arg with galaxy

in makeGalVMap:
    replace model arg with galaxy, detector, and psf
    compute inc from cosi rather than from diskBA and diskCA

in makeGalVMap2:
    replace model arg with galaxy and detector
    remove old commented galsim code defining galaxy image

in makeImageBessel:
    replace model arg with galaxy and detector

in makeConvolutionKernel:
    replace model arg with detector and psf

in vmapObs:
    model is retained as arg, but update attribute gets with
        sub-objects, e.g. model.obs.detector

in vmapModel:
    replace model arg with galaxy

in ellModel:
    replace model arg with galaxy
update plot functions with new classes in base.py

replace model arg with detector in drawGSObject and showImage
replace model object with galaxy object in test_ellModel0