Code to handle valid table creation and updates

[astrochun]

Something consistent for both Zcalbase_gal and Evolution of Galaxies

[astrochun]

@Reagen and @cmccormick1: We should discuss how best to do this through Metallicity_Stack_Commons

[astrochun]

Need to change compare_by_eye to use revised validation table instead of specifying in codes.

[astrochun]

Additional commits in: 4f3d677, 2002763

Also pulled develop and release/0.8.0 for consistency: 3e85dc7, 0988ee3

[astrochun]

For next release, we will need to fix compare_by_eye to use a table instead of defining each available sample via a set of np.where, which is currently done.

Update: Decided that it would be best in the current situation to implement in a new feature/validation_tables2 branch. Release 0.9.0 will be the default.