add new apis and samples

samples/widget_add_remove_sample.lua

@@ -1,11 +1,26 @@
 function on_resume()
-    ui:show_buttons({ "Add clock widget", "Remove clock widget" })
+    ui:show_lines{
+        "Add clock widget",
+        "Add clock widget (position 1)",
+        "Add clock widget (position 5)",
+        "Remove clock widget",
+        "Swap first and third widgets",
+        "Swap back",
+    }
 end
 
 function on_click(idx)
     if idx == 1 then
         aio:add_widget("clock")
-    else
+    elseif idx == 2 then
+        aio:add_widget("clock", 1)
+    elseif idx == 3 then
+        aio:add_widget("clock", 5)
+    elseif idx == 4 then
         aio:remove_widget("clock")
+    elseif idx == 5 then
+        aio:move_widget(1, 3)
+    elseif idx == 6 then
+        aio:move_widget(3, 1)
     end
 end