GUI: status bar rendering. Power: battery indicator. (#207)

* Menu: animation. Irukagotchi: idle image.
* Power: battery, usb activity widget
* Power: tune battery max voltage and clamp overshoot
* get initial charge state

Co-authored-by: Aleksandr Kutuzov <aku@plooks.com>
Co-authored-by: aanper <mail@s3f.ru>

applications/gui/widget_i.h

@@ -2,8 +2,31 @@
 
 #include "gui_i.h"
 
+struct Widget {
+    Gui* gui;
+    bool is_enabled;
+    uint8_t width;
+    uint8_t height;
+    WidgetDrawCallback draw_callback;
+    void* draw_callback_context;
+    WidgetInputCallback input_callback;
+    void* input_callback_context;
+};
+
+/*
+ * Set GUI referenec.
+ * @param gui - gui instance pointer.
+ */
 void widget_gui_set(Widget* widget, Gui* gui);
 
+/*
+ * Process draw call. Calls draw callback.
+ * @param canvas_api - canvas to draw at.
+ */
 void widget_draw(Widget* widget, CanvasApi* canvas_api);
 
+/*
+ * Process input. Calls input callback.
+ * @param event - pointer to input event.
+ */
 void widget_input(Widget* widget, InputEvent* event);