Input weights to the bipolar layer

Bipolar layers now receive equally weighted inputs from triad locations.
Added visualization for bipolar input weights
Bipolar layer, save functionality, git ignore

Bipolar cells can now update themselves based on cone and horizontal
activities, but the outputs don't look like what we want.  More testing
required.
Added a save functionality based on the pickle library.  Retinas can be
generated, stimulated, saved and loaded.  Save files are stored as .p,
and since these files are quite large, I've added "*.p" to the gitignore
file
Scalable pygame displays

Now the pygame windows scale up/down the retina to fit a 1000 x 1000 px
display
Visualization, Printing, Saving

Extended some of the above functionality, but mainly ran parameter
testing to get bipolars to respond