Make aplpy vs non-aplpy clearer

[keflavich]

Users see totally different behavior when aplpy is installed vs when it isn't when using quicklooks. The interface is awkward - if you make a quicklook, then want to modify it, you can do that w/aplpy but not really w/the non-aplpy version. We should probably remove the 'try aplpy / fail to other thing' approach and/or permanently deprecate aplpy.

OTOH, quicklook is meant to just be quicklook, not final display.