This will allow us to use this.$scrollTo in components. I'm now also
using this in the mixin. With so many `this`s it gets horribly
difficult to properly test the mixin in isolation. So I decided to test
the mixin on the component directly.
If we make this a mixin, we can re-use the same solution for e.g. the
comment. If sb. notifies you, the browser automatically scrolls to the
comment in which you have been mentioned.