Python 3 + Poetry + Github Actions testing

[jtratner]

@pkaleta cc @anujkumar93 - I noticed Travis CI was no longer polling repo, so I took. a bit of time to upgrade stor testing suite to use github actions.

Changes

• Switch to Github Actions - see workflow file - faster than travis / more integrated / has caching
• Switch to poetry for build tool - While trying to use github actions, I hit issues with virtualenv and friends, so I figured "Why not just upgrade to poetry because it's easier?" So... I did!
• Drop Python 2 support Finally, I realized that I was changing a bunch of things anyways, so I may as well drop Python 2 support (now that it's EOL anyways) so we can focus on developing with nice type annotations and such.
• Drop support for python 3.5 - We want to use f-strings.
• Fix hidden lint issues Lint issues are because (as usual) our version of flake8 was so out of date that it was just silently ignoring everything.

Future

• blackify repo - tired of dealing with dumb lint errors
• mypy type annotations - similarly, we should be doing types and such
• enforce import sorting - some way, preferably with automatic reordering.

[jtratner]

NOTE: one issue (currently) is that we will have to manually tag releases (similar to samwell). Ideally we'll make some kind of default action that auto-packages release notes and increments version BUT... for now this is what we got.

[jtratner]

Nvm - ditched python3.5 cuz I'd already used f strings

[pkaleta]

I've noticed there are some annotations failures, have you seen this?

[jtratner]

I've noticed there are some annotations failures, have you seen this?

This is because of an expected traceback that gets dumped in a test. Would be good to stop emitting it. Def good fodder for ticket

[jtratner]

One more PR incoming with some additional tweaks to get poetry fully working 😅