Wikia: handle 7z archives

[macbre]

• https://pypi.org/project/libarchive/
• https://github.com/dsoprea/PyEasyArchive#examples
• https://github.com/Changaco/python-libarchive-c#usage

Dumps

• https://s3.amazonaws.com/wikia_xml_dumps/p/pl/plpoznan_pages_current.xml.7z
• https://s3.amazonaws.com/wikia_xml_dumps/m/ma/macbre_pages_current.xml.7z