Separate the pagureio theme out into its own subpackage in pagure.spec
This makes the main pagure package just a tad bit lighter, and also
helps for showing how themes can be separately packaged.
Merges https://pagure.io/pagure/pull-request/3510
Signed-off-by: Neal Gompa <ngompa13@gmail.com></ngompa13@gmail.com>