Refactor Contacts public key import to be able to import many keys

[tomholub]

When you open FlowCrypt Settings -> Additional Settings -> Contacts -> import and you import a file with many keys, you will notice that the page will try to render each public key in its own iframe. That won't work well if the file you imported has 3000 keys for example, and we can't expect the user to press 3000 buttons.

I think we should stop using pgp_pubkey frames on the bulk import settings page, and instead have separate logic on Contacts page, designed for bulk.

• when I input a file, show Parsing, this may take a while.. (spinner)
• expect possibly several public keys contained
• expect that each public key possibly contains several emails
• render [N] public keys found containing [Y] user email addresses. [import all]
• after I click import all, there should be a progress percentage rendered as they are getting saved
• make sure that the UI doesn't get completely frozen on any step (parsing, rendering, importing) so that if I change my mind, I can still close the window

Originally posted by @tomholub in #2304 (comment)