Tags are not case sensitive.

This is friendlier to users. Worse, before, tags were SOMETIMES
treated case insensitively and sometimes not. Specifically the
database treats string comparisons as not case sensitive by default
(something I didn't know). But our PHP code used case sensitive
comparisons. Now, we are case insensitive hopefully everywhere.
Search keywords are not case sensitive.

I may rethink this, but people did get confused at SOSP.
UI tweak: Attachments get a separate header.