Bug 23642. Best effort mime detection for OpenXML files

Bug 23642. Best effort mime detection for OpenXML files

OpenXML files are Open Package Convention files. Internally, we use the custom mime application/x-opc+zip for these files. In the database, we store the 'proper' mime, which we gu
ess from the file extension, or if not supported, application/zip. All OPC files are blacklisted by $wgMimeTypeBlacklist by default, just as other zip files.