Improve Thunderbird "Feed Account" UX

[ator-dev]

After trying this for the first time, as a long time Thunderbird user, I have a few thoughts! 128.10.2esr.

Firstly, the initial dialogue is a little unattractive, and I don't know why it needs two steps when the first is "enter the account name" and the second is "this is the information you entered [it's only the account name], please check it". It gives the impression this will be hard to change later. Also, there's no padding between the Back and Finish buttons.

Next, once I'd done that, I had no clue what the effect of my action was. It turned out the new account doesn't show up in Unified Folders until you have at least one subscription inside it! This should definitely be fixed - some people, like me, only have Unified Folders enabled.

Finally, I had to consult online instructions to work out how to add a subscription. I completely missed the top button row, containing "Manage feed subscriptions", of the Feed account's start screen, because they blend in and don't look like buttons. This is a strange design choice because the buttons right below *do* look like buttons, which is misleading. Couldn't they have the same design?

Thanks!