Addition of Brown Dwarves into SPISEA

[caitlinbegbie]

This pull request incorporates all of the changes I have made to incorporate brown dwarf stars and their properties as both primary masses and companions. The main changes are as follows:

1. Expansion of lower masses available to be generated.
2. Updating of the IFMR class IFMR_Raithel18() and evolution model MergedBaraffePisaEkstromParsec in order to accurately incorporate BD masses.
3. Creation of a new compact remnant phase (phase=99) to classify BDs specifically and bring them into clusters with and without multiplicity.
4. New function to assign BDs with accurate effective temperatures using a table of known objects.

An outline of clusters generated with brown dwarf masses can be found in the notebook SPISEA/changes/BD_Clusters.ipynb.