Issue title: Edit channel/playlist url
 Issue body: Hi,

I've tens of channels and I want to edit channel/playlist url but ui doesn't accept this behavior. 
May you please enable editing channel/playlist url

Side question:
What's the type of TT database? I suppose it's not SQLite, is it true?
 Comments: 
 Comment 0: The Tartube database file is created by the [python pickle module](https://docs.python.org/2/library/pickle.html), so it's not SQLite or anything like that.
 Comment 1: Changing the URL of channels/playlists was added in v2.1.051.
 Comment 2: > The Tartube database file is created by the [python pickle module](https://docs.python.org/2/library/pickle.html), so it's not SQLite or anything like that.

I don't know what's the reason of using this module but I find it not a good/safe choice. SQL much better for modifying the options (in my case I want to modify many links) and much safer in case of crashing (my TT database corrupted many time and I'm sure if you used SQL it's nearly impossible to corrupt)
 Comment 3: > Changing the URL of channels/playlists was added in v2.1.051.

Thanks a lot
 Comment 4: >I don't know what's the reason of using this module but I find it not a good/safe choice. SQL much better for modifying the options (in my case I want to modify many links) and much safer in case of crashing (my TT database corrupted many time and I'm sure if you used SQL it's nearly impossible to corrupt)

I describe a "Tartube database", but it's not really a database. It's just a collection of data stored as dictionaries/associative arrays. Pickle is the standard python module for loading/saving this kind of data.

About SQL, I have nothing but bad experiences with it. I haven't experienced the TT database corruption you describe. You can create a new Github issue for that, if you like. 
 Comment 5: > You can create a new Github issue for that, if you like.
Unfortunately this issue is frequently occurs the bad thing I couldn't catch how this occurs to be able to create a ticket for it!
 Comment 6: Go ahead and create a ticket. Until now, it was not worth adding support for SQL. But if Tartube crashes a lot, while saving the database, then that's a good reason to add SQL support.
{'source': 'GithubIssues', 'repo_name_with_owner': 'axcore/tartube', 'issue_id': 648406230, 'repo_stars': 1268.0}