Naive maps updates

[petiay]

Added several options:

• Can now calculate the median of the BEAST results (instead of by default just the mean)
• Can make maps of three stellar parameters - for now they are log(T), log(age), and initial Mass. Easy to tweak or add more.
• Can input a chi2min threshold to cut BEAST stats before making maps
• Updated map file naming (from experience it's nice to know the map resolution at a glance esp. when there are comparisons with various ISM maps).

[karllark]

Overall looks good. Have a couple of comments that should be addressed.

[codecov]

Codecov Report

Attention: Patch coverage is 5.88235% with 16 lines in your changes missing coverage. Please review.

Project coverage is 14.75%. Comparing base (8d43cf9) to head (0b512d8).
Report is 21 commits behind head on master.

Files with missing lines	Patch %	Lines
megabeast/tools/make_naive_maps.py	5.88%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #71      +/-   ##
==========================================
- Coverage   15.21%   14.75%   -0.46%     
==========================================
  Files           6        6              
  Lines         355      366      +11     
==========================================
  Hits           54       54              
- Misses        301      312      +11     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[karllark]

Looks good to me.

[karllark]

No tests to speak of for megabeast yet. So ignoring these for now.