Replace tslint with eslint

[badsyntax]

Refs: #166

This change replaces tslint with eslint and uses the recommended rules provided by the @typescript-eslint plugin.

It also adds an option to add prettier as an eslint plugin. If enabled, prettier will be run through eslint, meaning formatting errors will be surfaced (and fixed) through eslint. You can see an example of how the project is genereated with prettier: https://github.com/badsyntax/vscode-generator-eslint-prettier-example

This approach is somewhat similar to the existing ext-command-js eslint setup, although there's no prettier option for that type. (Do you want me to add prettier to ext-command-js as part of this PR?)

[msftclas]

All CLA requirements met.

[aeschli]

Fixed by #192

[aeschli]

Thanks for the work, @badsyntax , sorry for taking #192 instead, which is a bit simpler.