Better scroll handling

[dwwoelfel]

The main change here is to keep the index page mounted in the dom when you navigate to a blog post. That lets us restore your scroll position when you navigate back to the index page.

A couple of minor changes:

1. Fetches 60 new posts instead of only 10 new posts per page
2. Uses a passive scroll listener, which lets the browser do some optimizations

[dwwoelfel]

Closing in favor of #256