Add possibility to change log level in runtime

[prajnoha]

We can define log level on SID startup with '-v' arg. But it may be useful for debugging, if we start logging at certain point and stop at another point in time that we can define. This could be done by sending a signal to SID daemon which in turn would set the log level.

Currently, we can set the log level only with log_init call, we will need to add a new log_change_verbose_mode fn to src/log/log.h interface (but that will just change the global _current_verbose_mode variable).