core/tags.cpp was WAY too big, so I moved this code into a new file in
its own directory. I also created a new unit test just for testing the
Artist tag.
This patch disables the "tags" test since it conflicts with the
tests/core/tags/ directory. This is okay because the tagdb is gradually
being phased out!
Signed-off-by: Anna Schumaker <Anna@OcarinaProject.net>