cmd_bar improvements (#4014)

- Split cmd_bar into 2 functions, improving errors and reducing strcmps
- Only update barconfig when something has changed
- Only update barconfig for the specific bar that has changed

Fixes #3958

include/configuration.h

@@ -425,9 +425,3 @@ bool load_configuration(const char *override_configfile, config_load_t load_type
  *
  */
 void ungrab_all_keys(xcb_connection_t *conn);
-
-/**
- * Sends the current bar configuration as an event to all barconfig_update listeners.
- *
- */
-void update_barconfig(void);