Remove kernel config from parent config files

those config files are no longer read by the kernel

- Allow `--help` and config_file class lists to differ (due to weird mixin behavior)
- Add `ipython_kernel_config.py`
- kernel config still shows up in `qtconsole --help`,
  but not in the `ipython_qtconsole_config.py`


- [x] Still need to check any docs that refer to putting kernel config in the parent app's config file.

closes #6533
I don't think so, I just did it for symmetry. I think `classes` are only used for these two things. Mainly it makes sense to customize whichever one should be longer, because you can do `return self.classes + [extra]` more easily than you can remove items.