Need to move Video library listing

[scotthmurray]

Now that video won't be included in the download, but is an external library, it no longer makes sense to list it as an "included library" on:

/processing-web/distribution/libraries/index.html

We need to figure out where to move this listing, which could involve restructuring the page to distinguish between:

• included libraries
• official external libraries (from the PFoundation)
• contributed external libraries (from 3rd parties)

[REAS]

I'm looping in @prisonerjohn This will probably need a phone call to sort out.

[prisonerjohn]

I see two ways of dealing with this:

• Add a new category, for example Foundation which we'll use for "official" libraries, tools, and modes. The page generator could then place these in their own section on the site. The system only supports single categories per entry now, so we won't be able to also put the library in the "Video & Vision" category.
• Add a new key-value pair to the contributions.txt file, for example source=foundation and use this to populate the different sections. source=external can be the default and we won't advertise it so that we don't need to worry about contributors misusing it.