We fixed the main issue of this form in CVE-2020-9444, but the audit
done at that time only included links found in rendered_markdown; this
change completes our audit for links with target=_blank anywhere in
the codebase.
Fixes the problem of recipient_bar_icons being too close to each
other. To improve spacing between them, classes are added, namely
recipient_bar_icon_link (for link icon) and reciepient_bar_icon
(for other icons). CSS for spacing these classes correctly, using
padding-left and padding-right, has been added zulip.scss
Manually tested for cases with single and multiple links present.
Fixes#14364.