Plot binary evolution improvements

[TomWagg]

Here are a couple of improvements/fixes for plot_binary_evol:

• Fix usage of gridspec to avoid double axes that overlap and confuse things (see screenshot of current docs page below)
• Add option to supply a t_min and t_max
• Add option to supply custom colours and labels for the ktypes

Here's a little test script to see how things work:

from cosmic.plotting import plot_binary_evol
import matplotlib.pyplot as plt

plot_binary_evol(bcm,
                 ktype_kwargs={'k_type_labels': ["TOM" for i in range(16)]},
                 t_min=100,
                 t_max=200)
plt.show()

Before:

After (different binary though):

[codecov[bot]]

Codecov Report

Attention: 310 lines in your changes are missing coverage. Please review.

Comparison is base (8772c07) 86.91% compared to head (454b07e) 87.74%. Report is 22 commits behind head on develop.

Files	Patch %	Lines
cosmic/src/assign_remnant.f	9.39%	193 Missing :warning:
cosmic/src/zfuncs.f	6.67%	84 Missing :warning:
cosmic/src/hrdiag_remnant.f	64.00%	18 Missing :warning:
cosmic/plotting.py	0.00%	13 Missing :warning:
cosmic/evolve.py	0.00%	1 Missing :warning:
cosmic/utils.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #611 +/- ## =========================================== + Coverage 86.91% 87.74% +0.84% =========================================== Files 40 42 +2 Lines 25542 25692 +150 =========================================== + Hits 22198 22543 +345 + Misses 3344 3149 -195 ```

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