Feature/337 slf4j logging

[digulla]

Notes:

• I didn't remove all calls to getLog() since some are used to set the flag "verbose". I don't know whether Maven will propagate the log level to all slf4j loggers.
• For the same reason, I left the "if (isVerbose())" before the log calls but removed most if (LOG.is...Level())
• I kept the if (LOG.is...Level()) is it protected a big code block.
• I replaced "..." + variable with "... {}", variable in all places I noticed. This should now be the default.
• I replaced "... +" Arrays.asList(x) where x is an array with "{}", (Object)x. Without the case, the Java compiler would try to copy the array elements into the varargs parameter of slf4j with the result that only the first element of the array would be logged.

[ppalaga]

Thanks for the contribution @digulla , comments inline.

[digulla]

The last two commits fix a deprecation and a warning I got in the POM. Since they are small changes, I didn't want to create a PR for them.

[ppalaga]

Summary: two last things open from my PoV:

1. org.codehaus.mojo.license.logback.* removal

2. <scope> in depManagement removal.

[digulla]

I'm now running out of time. I'll be at a conference next week, see you in July.

[ppalaga]

@digulla it is a pitty. This is not the first time that reviewing your large PR costs me time with no result. Please send PRs that have chance to get reviewed and merged quickly. Please discuss potentially controversial things like adding new dependencies upfront. To move forward with the next release, unless you veto within a reasonable time, I am going to make a new PR out of the acceptable parts of this PR.

[ppalaga]

Replaced by #342