Use local MIME database info
Python's mimetypes module is used for checking mimetypes in Catfish. It uses its own MIME database which differs from the local database. Checking xdg-mime query against mimetypes.guess_type often gives different results. And guess_type lacks many entries (when this happens it forces Catfish to check files it doesn't need to during fulltext search).
This checks for the /usr/share/mime/globs2 file generated by update-mime-database (from shared-mime-info) and allows Python's mimetypes module to use the local MIME results, matching xdg-mime (from xdg-utils).
This should keep the speed of guess_types but use a bigger and more accurate MIME list. It will give more accurate search results, help with file icon retrieval, and result in less disk reads (speeding up fulltext searches).