WIP: Overhaul key- and subscription-pages

Some changes inspired by the emails and conversations of the last days.

Keys have their own upload-page, subscriptions get a listing-page, a edit-page, and a create-page. The listings have been changed to better display the relevant information, not just something.

It's by far not finished, but I think the direction is right.

Please use the thumbs up/down to express your position towards a merge if you don't feel like discussing details.

Here are some screenshots to get an impression.