Fixed bug causing 'new item' to not work outside the root directory.
Icons specified in template files are now actually loaded.
Added icon for XmlContent template.
NewContentDialog must more attractive now. Displays template items in a ListView instead of a ListBox, and shows their icons.
Templates loaded from a subfolder of the search path were not correctly resolving the fullpath.
Fixing mac build.
Merge pull request #3005 from SickheadGames/NewItemImprovements

Improvements to 'New Content' dialog.