Updates to make project run out-of the box / assorted improvements

[amiller-gh]

Updated:

• Move optimization tests to their own directory.
• Simple template serialization does not wrap output in tag.
• Demo app now saves work between refreshes and has optimizer options.
• Bump postcss-selector-parser to 3.1.1 and remove link from bootstrap.

[amiller-gh]

This can be merged once postcss-selector-parser@3.1.1 is published: https://github.com/postcss/postcss-selector-parser/pull/123