Make the selection list position when in wizzy mode

This attempts to position the mention select box on screen when in wysiwyg mode

The issue seems to be the iframe, what is returned is the offset to that window, not the view window.  So this uses the reposition event that atwho triggers, and what it does is essentially take the returned offset values and adds them to the location of the iframe in the main window so we can position it to the main and not the iframe.

Also does a very basic above or below space check to locate the dropdown in relation to the selector.  Its not as spiffy as whats in the main plugin since this is for testing and not sure this works or not :innocent: 

ETA: moved the textbox mention.js out of themes and in to its own file, also moved the initialization of mentions in to post and display since those are the only areas that use it I think.

Small reorder to display.template in how optional js gets loaded