In order to genericize use of Zulip outside companies,
all instances of coworkers have been changed to users.
NOTABLE EXCEPTION: When the Zulip instance is domain-
locked, the reference to coworkers remains. The reason
for this is twofold: first, the majority of Zulip instances
which require a particular domain will be locked to a
company, and second, the template variable for the domain
necessary should be added to the alert so it is clear
to the user what the domain needs to be for access.
Fixes: #861.
Eklavya Sharma
Tim Abbott
Vishnu Ks
Rachel Kelly
Ashish Kumar