Autosuggest quest titles for plain text links

Displays a tooltip under the textarea that suggest to insert a linked quest title. The tooltip is displayed either when you type/paste a link, or when you put the cursor inside the link.
![screen shot 2013-09-08 at 5 19 40 am](https://f.cloud.github.com/assets/381895/1102484/c62cee98-1824-11e3-9b0e-fdf9d0ec6013.png)
I also replaced the `keyup` event with `input` event for `postEdit` handler. It's supported in WebKit, Firefox and IE9+.