improve Prompt and use it to ask for level and file name when exporting

code/ui/prompt.lua

@@ -18,6 +18,8 @@ Prompt = {
 	pos = { x = 10, y = 10 },
 	input = "",
 	name = "input",
+	canceled = false,
+	closing = false,
 	
 	active_prompt = nil,
 }
@@ -32,9 +34,12 @@ end
 function Prompt:keypressed(key, scancode, isrepeat)
 	if key == "backspace" then
 		self.input = backspace(self.input)
-	elseif key == "return" or key == "kpenter" then
+	elseif key == "return" or key == "kpenter" or key == "escape" then
+		if key == "escape" then
+			self.canceled = true
+		end
+		self.closing = true
 		self:func()
-		Prompt.active_prompt = nil
 	end
 end