Make quiet logging actually quiet

[regisd]

Currently, jflex has options

• --verbose which enables Out.println
• --quiet which negates --verbose

Options.verbose and Options.quiet are always the opposite of the other, except in the JflexTestRunner.

This is very confusing and this PR refactors Options and logging:

• Replace the Options.verbose and Options.quiet by Options.logLevel
• To match with current behaviour
  • the log level is WARNING by default
  • --verbose increases verbosity to Level.INFO
• Contrary to current behaviour --quiet will reduce verbosity to Level.SEVERE.
  • as needed by the JflexTestRunner
  • as wished by Bazel rule