Users can invite people to topics from secured category, but they will
not be redirected to the topic after signing up unless they have the
permissions to view the topic. This commit shows a warning when invite
is saved if the topic is in a secured category and none of the invite
groups are allowed to see it.
* FIX: Show resend button only if an email was sent
Otherwise, show the "save and send email" button.
* UX: Copy change
* UX: Show feedback when link was copied
The user interface has been reorganized to show email and link invites
in the same screen. Staff has more control over creating and updating
invites. Bulk invite has also been improved with better explanations.
On the server side, many code paths for email and link invites have
been merged to avoid duplicated logic. The API returns better responses
with more appropriate HTTP status codes.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
