diagnostic plots - add option for log(A_V)

[lea-hagen]

This adds an option in plot_input_data.py to use log10(A_V) in the histograms, with the idea of making it easier to visualize log-normal A_V distributions. The histogram bins are equal width in log space.

Also made a slight adjustment to the histogram plotting command to fill in the tiny gaps between each bar.

[coveralls]

Pull Request Test Coverage Report for Build 31

• 0 of 21 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.8%) to 17.925%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
megabeast/plot_input_data.py	0	21	0.0%
<!--	Total:	0	21	0.0%	-->

Totals
Change from base Build 30:	-0.8%
Covered Lines:	57
Relevant Lines:	318

---

💛 - Coveralls