Change verbosity to match log level

[zuckschwerdt]

Changes verbosity numbers (0-4) to match new log levels (1-8).
We default to a new level of 4 (WARNING) and each -v options increases the level by 1 unchanged.

The new level allow to distinguish between normal and abnormal state messages:

• FATAL (1): A fatal error. Not actually used, fatal errors usually fprintf and terminate. This is the highest priority.
• CRITICAL (2): A critical message. The user usually needs to see this.
• ERROR (3): An error. An operation did not complete successfully, but the application as a whole is not affected.
• WARNING (4): A warning. An operation completed with an unexpected result.
• NOTICE (5): A notice, which is an information with just a higher priority.
• INFO (6): An informational message, usually denoting the successful completion of an operation.
• DEBUG (7): A debugging message.
• TRACE (8): A tracing message. This is the lowest priority.

Note that we adopted the SoapySDR log levels but change CRITICAL to be a normal message.
We denote only FATAL, ERROR, and WARNING as abnormal. FATAL will terminate, ERROR indicates an important problem, and WARNING can likely be ignored.

This builds on #2263 and is preparation for #2254