Deprecate listing pages on portal

[ryguyrg]

The portal has moved to being a developer community home -- not the place that GraphGists should be browsed/searched.

The portal shouldn't need to display listings of Gists in categories/use cases/search/etc any longer. This should obsolete some of the other bugs and shrink the codebase.

I would only leave the ability to display a handful of gists on the homepage (under the featured section-- but focus on good gists that developers can use as an example, vs gists for end-users)