small changes for code readability

[lea-hagen]

Changing some variable names to make the code easier to understand (at least for me?):

• beast_on_lnp is now lnp_grid_vals: this holds the dictionary in which each key is a fitted BEAST parameter, and each value is an array (shape = (n_lnps, n_stars)) that holds the parameter associated with the sparsely-sampled lnps for each star
• model_weight (in ensemble_model.py) and dustpriors (in megabeast.py) are now beast_dust_priors: this is the PriorWeightsDust object

I also added the new distance parameter to the default list in read_beast.

[coveralls]

Pull Request Test Coverage Report for Build 29

• 2 of 17 (11.76%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 18.75%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
megabeast/megabeast.py	0	3	0.0%
megabeast/plot_input_data.py	0	3	0.0%
megabeast/beast_data.py	0	4	0.0%
megabeast/ensemble_model.py	2	7	28.57%
<!--	Total:	2	17	11.76%	-->

Totals
Change from base Build 28:	0.0%
Covered Lines:	57
Relevant Lines:	304

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💛 - Coveralls