Apparently, we didn't have one of these, and thus had a moderate
number of generally very old violations in the codebase. Fix this and
clear the ones that exist..
I think this will fix a Casper flake where there was a race
window with multiple temp DOM elements holding copied text.
I also add a comment to the code I think causes this race
for the tests.
Algorithm for copying messages from serveral topics was changed:
- if there are selected messages from more than 1 recipient block
then the recipient bar headers are copied;
- If there are multiple messages from only one recipient block
then recipient bar header is not copied.
Fixes#7217.
Also adds a full suite of Casper tests for the copy-paste functionality.