Standardize Typescript styles between all repos.

[shane-tomlinson]

Now that we are using Typescript in no less than 3 repos, we should determine a common style to share amongst all of them.

cc @bbangert, @ianb, @lmorchard

Ref #808 which is for Javascript.

[lmorchard]

FWIW, not that these have to be the rules we go with, but we merged in some TypeScript tweaks for eslint over on fxa-payments-server that might be a good starting point:

https://github.com/mozilla/fxa/pull/1357/files#diff-c9d5d4a598222f97e617f9c80fd7837c

Basically, just @typescript-eslint/recommended with a couple of tweaks for indentation and to match existing code.

[bbangert]

For pure typescript repos, I went with the recommended lint settings, but the type/interface rules are weird in that it wants to make all type aliases into interfaces. There's some disagreement about the rationale for doing this in modern Typescript so we should probably opt out of this one.

See: palantir/tslint#3248 and https://medium.com/@martin_hotell/interface-vs-type-alias-in-typescript-2-7-2a8f1777af4c

I also have seen good rationale for not using I in front of every interface, even though tslint recommended wants it. This styleguide says not to use I in front, and has some additional guidance on types vs interfaces at least: https://basarat.gitbooks.io/typescript/docs/styleguide/styleguide.html

[vbudhram]

from mtg:

Moving to next train.

[dannycoates]

done