Cache property

[Chadys]

I propose to use cached_property on all, if not most of seo properties.
Some properties are accessed several times in the template, and so provoke unnecessary duplicate db queries.

[vsalvino]

I did make the change, but it was mysteriously failing on certain unit tests. If you'd like to work on it and get the unit tests passing, that would be helpful!

[Chadys]

@vsalvino Sorry, didn't see your answer.
I don't think I'll have time to try it at the moment, if anyone else is interested, feel free :)