Allowing the users to append their filters into the existing BEAST filter library

[galaxyumi]

This PR is to allow the users to add any filters that are not in the default BEAST filter library into the filter library from command line. An input ascii file for a filter throughput curve should have two columns: wavelength in angstrom and throughput.

[codecov-commenter]

Codecov Report

Merging #756 (eae674a) into master (f206c52) will decrease coverage by 0.05%. The diff coverage is 12.50%.

@@            Coverage Diff             @@
##           master     #756      +/-   ##
==========================================
- Coverage   43.31%   43.26%   -0.06%     
==========================================
  Files         101      101              
  Lines        9811     9825      +14     
==========================================
+ Hits         4250     4251       +1     
- Misses       5561     5574      +13     

Impacted Files	Coverage Δ
beast/observationmodel/phot.py	36.48% <12.50%> (-1.50%)	:arrow_down:
beast/tools/subgridding_tools.py	32.59% <0.00%> (-0.38%)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update f206c52...eae674a. Read the comment docs.

[karllark]

This PR supersedes PR #646, right? If so, please confirm that it provides the same capabilities or that those are not needed desired anymore.

[karllark]

Ping.

[karllark]

Ping. ;-)

[galaxyumi]

Ping. ;-)

Sorry!! Yes.