Use the stats partial for both the authority and search results

I've had a play at making a unified sidebar partial and while it's possible, I'm not sure it's actually better to have 1 complicated partial rather than 2 relatively simple ones.

For now, I've broken the authority sidebar code out into it's own partial and made the 2 sidebar partials' structure more similar. The stats partial is now shared between the 2.

Closes #145