Axis limits are hard-coded in expression plots

[caiw]

Should be generated from data, with optional arguments to force.

[neukym]

My suggestion, instead of line 43 in plotting.py

if ylim is None:
            ylim = 10 ** -100

something like (apologies for pseudocode):

if ylim is None:
        lowest_pvalue = lowest_pvalue_of_all_functions_in_show_functions_from_both_left_and_right_hemi
        if lowest_pvalue <= 10 ** -100:
            ylim = lowest_pvalue + 10 ** -10
        else:
            ylim = 10 ** -100

[neukym]

As an aside, @ollieparish has found the first sub- 10 ** -100 function already...

[neukym]

Closed with #55