Get Rid of Pandas Dependency

[xcthulhu]

pandas is a really heavy python library requiring ~10 minutes of compilation

It is only used in one place:
https://github.com/TESScience/FPE/blob/master/tessfpe/data/housekeeping_channels.py#L49

It should be noted that pandas.DataFrame.to_string can easily be replaced with the unix column utility.

Since this is only used in one place, we should consider a slight refactor to avoid using pandas all together.

It should be noted that numpy is also only used in this one place in housekeeping_channels.py, however we presumably will require matplotlib to resolve #15 which requires numpy as a dependency.