Factor out item reload code

Adds a new function io_reload_data() which can be used to reload all
appointments and TODO items.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/calcurse.h

@@ -797,6 +797,7 @@ void io_save_cal(enum save_display);
 void io_load_app(struct item_filter *);
 void io_load_todo(struct item_filter *);
 void io_load_data(struct item_filter *);
+void io_reload_data(void);
 void io_load_keys(const char *);
 int io_check_dir(const char *);
 unsigned io_dir_exists(const char *);