Find less magic looking numbers for cartesian grids

[clintval]

nucleic/nucleic/figures.py

Lines 47 to 48 in 8a3033e

	ax1_grid = GridSpec(rows=1.2, columns=1, i=0, rowspan=1, j=0, columnspan=1)
	ax2_grid = GridSpec(rows=4.8, columns=1, i=3, rowspan=1.775, j=0, columnspan=1)