dillon1000/react

[be] non-blocking ESLint config, fixes

Configures typescript-eslint for the project with an initial configuration that 
starts with their recommended rules, and adds/disables a few (generally either 
disabling warnings or promoting them to errors). The new `yarn lint` command is 
not hooked up to CI yet, so for now this is something we can opt-in to running 
locally. If you have some free time, help get us down to zero errors! 

My general philosophy for linting, which I propose we follow, is that lints 
should be very high-signal: 

* Error, don't warn. If it's worth mentioning it's worth fixing. 

* Enable rules that consistently identify real problems. If we frequently would 
have to disable the rule due to false positives, it isn't high-signal. 

* Enable rules that help improve consistent style (to avoid code review about 
style rather than substance).