Add support for Wiki Loves Folklore
Wiki Loves Folklore is another federated photo contest,
in scope of the wikiloves stats tool.
https://commons.wikimedia.org/wiki/Commons:Wiki_Loves_Folklore
- Add URL route to Flask app
- Add logo to Jinja templates
- Add scope to constants in functions.py and mainpage.html
- Update test fixtures and unit tests
Bug: T313588