Run user select Js only where needed

Transform current implementation into regular Coffescript classes
so that the same call method can be reused on the dispatcher
as for other classes.

Same rationale as: https://github.com/gitlabhq/gitlabhq/pull/8123

I have built the map by grepping for the touched classes + testing it out.

**Double check**

That I didn't make any mistakes when converting the existing coffee into classes.

The only changes are:

- `formatResult` and `formatSelection` became instance methods. For this to work, callbacks that use them need to bind with `=>` instead of `->` ( to avoid repeating class names by using the binded `this`)
- removed the prefix from instance methods, e.g. `userFormatSelection` became just `formatSelection` since it is already inside the `UserSelect` class