unify logging configuration

[trichter]

This PR tries to unify the logging configuration.
All calls to logging.basicConfig inside the library are deleted and some loglevel keywords are removed. Logging should be configured in the user's code. A simple logging.basicConfig() is often good enough. I added the NullHandler to the obspy's root logger 'obspy' so that by default no logging is emmited. Logging is only configured displayed for obspy-runtests -v.

WIP: If this PR is endorsed I would further refine it.

PR Checklist

• Correct base branch selected? master for new features, maintenance_... for bug fixes
• This PR is not directly related to an existing issue (which has no PR yet).
• If the PR is making changes to documentation, docs pages can be built automatically.
  Just remove the space in the following string after the + sign: "+ DOCS"
• If any network modules should be tested for the PR, add them as a comma separated list
  (e.g. clients.fdsn,clients.arclink) after the colon in the following magic string: "+TESTS:"
  (you can also add "ALL" to just simply run all tests across all modules)
• All tests still pass.
• Any new features or fixed regressions are be covered via new tests.
• Any new or changed features have are fully documented.
• Significant changes have been added to CHANGELOG.txt .
• First time contributors have added your name to CONTRIBUTORS.txt .

[trichter]

This PR is ready for review. I also added the possibility to specify a second -v flag in obspy-runtests. One -v will just display warnings. Two -v will use the verbose mode of runtests.

Closes #2625.

[heavelock]

Changes in obspy/signal/tf_misfit.py seem to be unrelated.

[trichter]

Changes in obspy/signal/tf_misfit.py seem to be unrelated.

Yes, these changes just deal with a DeprecationWarning of matplotlib. Are only related, because both warnings and logs show when running obspy-runtests.

[heavelock]

I just took again a look on this PR and I though about something that new. Why only deprecation since it's targeting master?
I think you could add deprecations to the 1.2.3 and here just drop it completely.

[trichter]

Thanks for having a look. I am all for fast depreciation, but I think most people favor a slower pace with depreciations only for mayor versions. IMHO this is ready for merging.

[ThomasLecocq]

look OK if all tests 🟢