Add Icon Picker Widget

Provided a patch which adds a new Element/Widget that utilizes the jQuery Font Icon Picker.

The logic was inspired by the fontawesome_iconpicker_widget sub-module within the fontawesome module.

I decided to place all the logic in a iconpicker sub-module, but technically the logic could be moved into the main module.

Fixed issue with the CSS of the icon picker being added after some of the icon sets' CSS leading to broken icons being displayed.

Fixed issue where the element validation was incorrectly attempting to validate empty values.