When I select one tag, and then a second the app should only display those
photos that have both tags.  Example, I'd like to see all pictures of both my
wife and I, I have attatched a tag for each of us to every picture that we are
in.  For pictures that just contain her only her tag is present, if we are both
in the photo both the tags are attatched.  When I select both her tag and my tag
my expectation is to see only those photos that we are both in, instead of all
the photos that either one of us are in.