Fixed: Deleting wave files not possible #313

Right click menu delete in resource view was limited to textures and folders only. Right clicking will highlight a row.

All resources can be deleted now with the right click option. Deletion works as follows: Right clicking will highlight a single item and delete it when it is outside a selected range of items. If the right click occurs outside a selction without a valid item the selection will be deleted. Behaves like in XCode's project navigator.