Add footprint functions into utils

[catherine-martlin]

See wfc3_gyro/plots.py

[mgennaro]

It seems that the footprints_plot has a dependency that is not included and may bot be necessary:

import unicorn.survey_paper as sup

I am commenting those out for now because I get an error when I try to import get_flat from the utils.py module. Will address this when I start working on the plotting routines.

@ivastar
can you comment on what sup is used for? Looks like it's got some positional info on the CANDELS (I guess) fields, and maybe info on the shape of the fields (I see you use this in conjunction with the shapely library)