[ENH]: Next release TODOs

[asreimer]

• [x] Upgrade to python 3.8
• [x] Deprecate python 2
• [x] Add seaborn
• [x] Add sunpy
• [x] Add pyephem
• [x] Add skyfield
• [x] Investigate using ubuntu 20.04 base image for resen-base
• [x] Make sure we install jedi 0.17.2 in the py38 enviroment
• [x] check if we can install npm with apt-get

Targeting release date: 15 November 2020

[asreimer]

Done all original checklist items.

New tasks:

• [x] update citation helper json file for newly installed python packages? (yup! #62)
• [x] build and test resen-core in #61
• [x] update docs
• [x] update tutorials
• [x] server integration

[asreimer]

Release To Dos:

• [x] update release date in docs right before releasing
• [x] update the cores.json file