Minor improvements to Channel groups

[shuvashish76]

Describe your suggested feature

1. Change it to "(=)" icon as modern design (similar to what we use for sorting in Navigation bar)
2. Show total number of subscriptions used in a group. Reason: Makes easier to recognize when recreating groups. Newpipe show the number for groups so the user can be sure that they picked all their channels for specific group.
3. Add confirmation dialog when deleting a group. Reason: It takes some time to create them & deleting by misclick is annoying.

Other details

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• I have written a short but informative title.
• I will fill out all of the requested information in this form.

[Bnyro]

Some oft them were already suggested in #3558, please ask to append the remaining suggestions there.