add new apis and samples

samples/screen-state-widget.lua

@@ -0,0 +1,48 @@
+-- name = "Screen state"
+
+local json = require "json"
+
+function on_resume()
+    ui:show_buttons{
+        "Save screen",
+        "Restore screen",
+    }
+end
+
+function on_click(idx)
+    if idx == 1 then
+        save_state()
+    else
+        restore_state()
+    end
+end
+
+function save_state()
+    local state = aio:get_active_widgets()
+    local json_str = json.encode(state)
+
+    files:write("screen-state", json_str)
+    ui:show_toast("Screen state saved!")
+end
+
+function restore_state()
+    local json_str = files:read("screen-state")
+    local state = json.decode(json_str)
+
+    remove_all_widgets()
+
+    for k,v in pairs(state) do
+        aio:add_widget(v.name, v.position)
+    end
+
+    ui:show_toast("Screen state restored!")
+end
+
+function remove_all_widgets()
+    local curr_state = aio:get_active_widgets()
+    for k,v in pairs(curr_state) do
+        if (v.name ~= "screen-state-widget.lua") then
+            aio:remove_widget(v.position)
+        end
+    end
+end