Add inheritance for social links.

[LimitedEdition1]

This allows for social links to be either inherited from config.toml, specific for each page, or completely disabled per page.

[budparr]

I like this idea, @LimitedEdition1 Thank you. I'm wondering if we need the global scope on the param here, $.Param "twitter" instead of .Param "twitter"

[LimitedEdition1]

I have it working on one of my sites with .Param "key" and seems to do what I expected. I could test the other way too.

[budparr]

I would think without it the param would only access it in front matter, not config. I could be wrong though!

[LimitedEdition1]

I just did a quick test and they both seem to do the same thing. A live Netlify site works without the $, but
perhaps the $.Param "key" is a preferred method.

[budparr]

I think it's fine. I suppose it only needs that scope when it's inside of the context of something else.