Refactor config

[leotrs]

This is one of a series of PRs aimed at fixing #337. This PR does a few things:

1. Introduces the tempconfig context manager. This works as follows:

      c = Camera()
      c.frame_width == config['frame_width']        # -> True
      with tempconfig({'frame_width': 100}):
          c = Camera()
          c.frame_width == config['frame_width']    # -> False
          c.frame_width == 100                      # -> True

   So it temporarily changes the config so that all classes that use it for default values will use the new (temporary) config. After
   the with statement ends, the config is restored. This accounts for the diff in config.py, __init__, and test_config.py. I remember @PgBiel in the past requested the feature of changing the global config. Now we can do it!

2. The problem with the code above is that Camera instances used the value of frame_width that was available at the time when the Camera class was being defined, not the value of the config at the time that the instance was being constructed. So I had to remove a few keys from Camera.CONFIG and set them in Camera.__init__ instead. I did it in a way that it will later be easy to change to attrs cc @PgBiel. This accounts for the diff in camera.py and test_camera.py

3. For some reason my changes made a difference in test_logging.py. I made it so that this test doesn't care about whitespace in the logs and now it works. I believe this is a fair change for now since apparently Refactored tests and added new tests tools for videos-tests. #335 is going to deprecate how tests currently work. cc @huguesdevimeux

Hope this makes sense! This is just the first in a few PRs concerning the config system.

[huguesdevimeux]

For some reason my changes made a difference in test_logging.py. I made it so that this test doesn't care about whitespace in the logs and now it works. I believe this is a fair change for now since apparently #335 is going to deprecate how tests currently work.

I think @Aathish04 is better to take a look at that, as he wrote these tests.

But personally, this seems very fine to me. (Nevertheless, #335 does not aim to change logging tests, not atm)

[huguesdevimeux]

Your test fix is I think not good.
I think it's because the log_width parameters in the config is not right, as it should be set to 512.
One way to fix it would be to create a custom .cfg with log_width = 512 and to use it in the CLI in the logging test. That's what I did in #335

cc @Aathish04 (author of this test)

[leotrs]

Ok, fixed the tests thanks to @Aathish04.

Now we need one more approval.