With this change I've gone through all ESLint rules at:
http://eslint.org/docs/rules/ and added all of them that I feel make
sense to the project.

This will allow us to focus on business logic of our code, rather than
on style discussions, which are now better guarded thanks to ESLint and
clang-format.

On the final note: it does not matter what concrete lint rules are
enforced (e.g., semicolons or nor). The important part is that they are
enforced by a tool and we do not spend time dicussing about them.

Addresses: #66