Fix bug where Find/Replace and FindInFiles search bars might be open at
same time for an instant (one sliding in while the other sliding out). Since
more of the UI uses overlapping names now, that causes more problems than
in the past.
Ideally, ModalBar would enforce that only one is open at a time, but the
close() options are too tightly controlled by the clients right now
(especially QuickOpen). So we use a side channel to ensure that the two
modal bars that now conflict directly (FindReplace, FindInFiles) don't
overlap.

Also, small cleanups: use double quotes in HTML templates; use underscores
for FindReplace APIs intended to be called only by FindInFiles.