Add search bar to team member list

Another thing we did for templates, when they started to get
unmanageable, was add a find-as-you type search. We’ve observed real
users interacting with this to great effect, so I think it makes sense
for users too.

Like for templates, it only shows up when there are more than 7, so that
it’s not clutter for teams who don’t have a lot of members.

app/main/forms.py

@@ -735,6 +735,11 @@ class SearchTemplatesForm(StripWhitespaceForm):
     search = SearchField('Search by name')
 
 
+class SearchUsersForm(StripWhitespaceForm):
+
+    search = SearchField('Search by name or email address')
+
+
 class SearchNotificationsForm(StripWhitespaceForm):
 
     to = SearchField('Search by phone number or email address')