application: Propagate verbosity to main instance

If another instance of calls was already running, invoking calls with
`-v` flag would set the verbosity for the newly created process and then
exit if it was not the primary instance.

src/calls-log.h

@@ -39,3 +39,4 @@
 void  calls_log_init               (void);
 void  calls_log_increase_verbosity (void);
 guint calls_log_get_verbosity      (void);
+int   calls_log_set_verbosity      (guint new_verbosity);