Add root imports with tilde prefix

Created by: selbekk

This commit adds babel-plugin-root-import to the default .babelrc file to define ~ as the absolute path to the src/ folder.

This gives us the possibility to turn code like this:

import SomeUtility from '../../utils/some-utility'

to this

import SomeUtility from '~/utils/some-utility';

The main upside of using this pattern in contrary to the approaches suggested in #741 (closed) is that it highlights what is a local import and what is a node_module import.

Fixes #849 (closed).