Template based icons for resource tree in modx revo 2.3

This enables the icon field in the template manager. It has been there for years but never been enabled. Every fontawesome iconclass (v 3.2.1) added here will result in an icon that is displayed instead of the default icon.

Example: icon-heart for the "love" template.

![love](https://f.cloud.github.com/assets/667315/1784732/86d02892-68d7-11e3-8743-1305c55db52d.png)

A list of all available icons can e found here: http://fontawesome.io/3.2.1/icons/