Allow sorting of documents in project embeds

[eyeseast]

Some options:

• alphabetically, by title
• by date, ascending or descending

Docs: https://help.muckrock.com/Search-19ef8892696381b7a95ccfbb4693d92b#19ef8892696381ee9951fb17e4173805

Note that embeds (and projects in general) hit the search API, so sorting happens using a Solr query. We need to make sure sort:title is included, for example.

[eyeseast]

The core of this is done but there's no UI. I'm going to leave it open in lieu of a new issue.