Allow usage of external tslint npm module

[microsoft]

Allow usage of external tslint npm module

[poelstra]

This is somewhat related to https://github.com/Microsoft/vscode-typescript-tslint-plugin/issues/78, which is about automatically walking tsconfig.json extends fields to find the 'right' version of tslint to use.

[octogonz]

I agree with @poelstra . When you have hundreds of projects in your monorepo, you want to minimize the amount of boilerplate that has to be copy+pasted into each project. If we can discover the location of tslint based on tslint.json (e.g. by following the extends property), that's one less setting to manage.

[haugerbr]

I'm going to go ahead and close this since tslint is deprecated in favor of eslint and the eslint plugin supports this already.