RFC: Turn Playing Time function into plugin

Since this function already requires hitting the
disk, it may make sense to turn it into a plugin.

A minor advantage (apart from cleaning up onplay.c
and saving RAM) is that you can now access the menu
not just from the WPS context menu, but also from
the Shortcuts Menu or using the WPS plugin shortcut.

On the other hand,  TSR plugins would have to be
terminated when Playing Time is launched, as is
already the case for other plugins such as PictureFlow.

Change-Id: Iea85229486887463ffc52f05e33e2340437f69a4

apps/plugin.h

@@ -958,6 +958,17 @@ struct plugin_api {
     /* new stuff at the end, sort into place next time
        the API gets incompatible */
 
+    const char* (*format_time_auto)(char *buffer, int buf_len, long value,
+                                    int unit_idx, bool supress_unit);
+    char* (*output_dyn_value)(char *buf, int buf_size, int value,
+                              const unsigned char * const *units,
+                              unsigned int unit_count, bool binary_scale);
+    int (*playlist_get_resume_info)(int *resume_index);
+    int (*playlist_get_track_info)(struct playlist_info* playlist, int index,
+                                   struct playlist_track_info* info);
+    bool (*list_do_action)(int context, int timeout,
+                           struct gui_synclist *lists, int *action);
+    int (*talk_idarray)(const long *idarray, bool enqueue);
 };
 
 /* plugin header */