GUI: abolish API injection into instances. (#265)

* GUI: abolish API injection into instances. Update usage by 3rd party apps.
* GUI: update documentation. Cleanup api usage. Adjust status bar item spacing.

applications/gui/icon.h

@@ -6,16 +6,38 @@
 typedef struct IconData IconData;
 typedef struct Icon Icon;
 
+/*
+ * Allocate icon instance with const icon data.
+ * always returns Icon or stops system if not enough memory
+ */
 Icon* icon_alloc(const IconData* data);
 
+/*
+ * Release icon instance
+ */
 void icon_free(Icon* icon);
 
+/*
+ * Get icon width
+ */
 uint8_t icon_get_width(Icon* icon);
 
+/*
+ * Get icon height
+ */
 uint8_t icon_get_height(Icon* icon);
 
+/*
+ * Check if icon is animated
+ */
 bool icon_is_animated(Icon* icon);
 
+/*
+ * Start icon animation
+ */
 void icon_start_animation(Icon* icon);
 
+/*
+ * Stop icon animation
+ */
 void icon_stop_animation(Icon* icon);