Fix disabled providers

[getzze]

Remove 'addic7ed' and 'napiprojekt' from the list of disabled providers.

Fix a bug happening when using subliminal as a library for scripting and a new provider is defined.
You needed to add the new provider to the default_provider list to be able to download subtitles easily.

>>> class MyProvider(Provider): pass
>>> provider_manager.register('myprovider = __main__.MyProvider')
>>> subtitles = list_subtitles([video], {Language('hun')}, providers=['myprovider'])
# a list of subtitles from myprovider matching the video.
>>> download_subtitles(subtitles)
# nothing happened, because myprovider is not in the default list. You needed to use:
>>> download_subtitles(subtitles, providers=['myprovider'])
# subtitles are downloaded
# with this PR, no need to add the 'providers' argument to 'download_subtitles'

Now the default_provider list is computed dynamically.
This was not affecting the CLI.