update frontend tooling

[alicewriteswrongs]

A lot of the frontend stuff in Micromasters is pretty behind what we're using elsewhere. We're on a pretty old version of node, using flow, outdated versions of babel, etc. Some stuff we should take care of:

• update nodejs version
• update eslint config
• upgrade yarn to v3
• convert Flow code to Typescript
• look into switching from Mocha to Jest