Configure unified tslint rules for the frontend and backend

[Fabianopb]

In the application's template, currently only the frontend has a tslint.json determining the rules, although the linter is running also in the backend. I'm guessing that the backend is deducing the rules from the frontend.

It would be nice to have shared rules applied for both the frontend and the backend to keep the project consistent. This could be done by creating a local library with the common tslint rules (in the same level as the frontend and backend folders) and importing that to both projects via yarn link.