Add logging verbosity slider

[djp952]

The standard logging verbosity has been pointed out to be a little excessive, and of course the new (1.2.8) 'verbose' logging is insane by design. Add a slider to the settings to allow for three levels of logging:

• Errors Only
• Standard (come up with a fancier name)
• Verbose (also come up with a fancier name)

[djp952]

I'm going to get rid of the semi-recently added 'transfer' logging, this doesn't feel appropriate anymore. Closing.