Attaching more than one SSH public key to the same account is useful,
e.g. if one uses different machines to access the AUR SSH interface.
Multiple keys can now be specified by adding multiple lines to the text
area on the account edit form.

Implements FS#45469.

Signed-off-by: Lukas Fleischer <lfleischer@archlinux.org>
Acked-by: Leonidas Spyropoulos <artafinde@gmail.com>