Generate a new UUID

Property definitions

nitc $ PbxUUIDGenerator :: next_uuid
	# Generate a new UUID
	fun next_uuid: String
	do
		seed += 1

		var hex_val = seed.to_hex.to_upper
		return "0"*(24-hex_val.length) + hex_val
	end
src/platform/xcode_templates.nit:69,2--76,4