Add The Stocks to Photography Collections

[plainspace]

This PR adds The Stocks to the Photography sections and adds a sub-section called Photography Collections.

[neutraltone]

Nice add, one thing, i've actually been adding aggregated content sites to the aggregated content section as these websites might not always be exclusive to photos.

I'm torn as to which is a better approach.

[plainspace]

@neutraltone your call! just lmk... I'd love to contrib.

[neutraltone]

Cool, would you be able to instead add "The Stocks" to the existing aggregated section and I will raise and issue to assess how things are at some point. That way if the aggregated section gets any longer I can think about moving it to your proposed method.

Thanks!

[plainspace]

Sounds good. Lmk what you think.

[neutraltone]

Good stuff, cheers!

I'll have a think about issue #88 and probably tackle a load of them over the weekend.