Add article index page and provide path for search engines to crawl it

[alexbainter]

Closes #40.

Creates a list of all articles when /find_articles isn't provided a datatype:

Also adds a link to it from the home page (below "Find Article"):

As the number of articles grows, we'll need to build on this (grouping articles by category, etc), but I think this is the perfect first step to make the articles crawlable.