add a follow/unfollow button next to the userlink

So this adds a `follow` or `unfollow` link that triggers the pertinent
event when clicked. So the approach I've taken is to add a method to
every userlink, but I don't know if it is the correct approach, the way
it works now is it'll check if it is you, if it isn't it'll check if
you're following or not and then put the link with the action needed
right beside it.

What's cool is that since we're using mercury every other link auto
updates if you move from following to unfollowing and viceversa. So
that's neat.
swap `follow`/`unfollow` with something less intrusive

replaces the follow or unfollow link with a glyphicon (plus sign) and
completely removes the unfollow possibility from there as it is an
action that will likely be used less frequently and could be performed
from the user profile always
add bubble notification to give the user feedback

Exposes a model `bubble` with the properties msg, type and show to
display notifications much like the disconnected from the back end one
usually you don't want to manage the `show` everywhere, instead you want
to have it in one place only and be automatic.

I am using it in `follow` and `unfollow` events only but in theory it
could be used for any event that needs notifying. There is one caveat
only: each notification overwrites the previous one, so there is no
stacking notifications.
Merge branch 'follow-button' of https://github.com/rcsole/phoenix into rcsole-follow-button

Conflicts:
	web_frontend/src/home/handlers.js
Merge branch 'rcsole-follow-button'