Feature Request: New MentionView design.

[hotoo]

I'm update simple-mention to 1.0.0，and it looks like:

I suggest MentionView design same the TagsView or TagCloud view will be more useful:

1. List view show all of the @mentions, and count mention times.
2. Click list item and use internal search funtions.
3. Click @mentions in notes, also use internal search functions.