Repositories bug fix

* Remove code that tries to detect repo name from other existing repos
* Automatically enable repo after it is added
Fixes #13602

Repository preferences: style fixes and use BUrl

Signed-off-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

Fixes #13194

Add the new Repositories preflet.

Also includes changes to HaikuDepot to change wording and add the menu item
to open the Repositories preflet.

Signed-off-by: Augustin Cavalier <waddlesplash@gmail.com>
Closes #13147.