Missing or malfunctioning block templates

[vossisboss]

There are blocks included in the starter kit that are lacking functional frontend html templates, which essentially makes them a lot harder for new users to use them in StreamField and elsewhere.

We should either provide basic templates for these blocks or remove the blocks that do not have functional templates if we aren't planning to support them.

The blocks that are missing templates or have templates that do not function include:

AccordionBlock
InternalLinkBlock
ArticlePageLinkBlock
ExternalLinkBlock
LinkStreamBlock
QuoteBlock
CardBlock
FeaturedArticleBlock

No doubt some of these are intended to be internal or base block structures. But we should at least add some basic demo code for any of the blocks we include so that people can see how they are supposed to work.

[vossisboss]

All right, I've so far added PRs for:

AccordionBlock
QuoteBlock
CardBlock
ImageBlock

I've also addressed some block code that could be cleaned up in #45 and #46.

The only one left I really want to add a template for is FeaturedArticleBlock. I'll be working on that next.