Group subscriptions and bookmarked playlists by service

[TotalCaesar659]

Checklist

• [x] I checked, but didn't find any duplicates (open OR closed) of this issue in the repo.
• [x] I have read the contribution guidelines given at https://github.com/TeamNewPipe/NewPipe/blob/HEAD/.github/CONTRIBUTING.md.
• [x] This issue contains only one feature request. I will open one issue for every feature I want to request.

Describe the feature you want

Separate all subscriptions and bookmarked playlists by service to collapsable groups.

Is your feature request related to a problem? Please describe it

When there are many subscriptions and bookmarked playlists, it's very hard to find which service they are belong.

Additional context

This is the example of subscriptions window with 5 ones from 5 services. Before: After:

How will you/everyone benefit from this feature?

NewPipe users will get the opportunity to hide subscriptions and bookmarked playlists from services that are unnecessary at the moment, especially there are very many of them.