Improvements to Icon Editor

* Added DModelPanel.FarZ member
* Removed broken model browser from Icon Editor
* Moved spawn icon behind the DModelPanel, so DModelPanel is usable with
big icons
* Added render button
* Moved skins from List to dropdown
* Added background to the DModelPanel
* Added Center positioning option ( Sets camera to origin )
Fixed util.worldpicker

It was only picking what's under the crosshair, now it works normally.
Worldpicker is back for Icon Editor
Merge pull request #558 from robotboy655/icon_edit

Improvements to Icon Editor