Render page titles for /mf2/ entries

A long-term issue has been that since adding /mf2/ entries, we've not been rendering their page titles. This also means that /search/ was populated with a load of empty unclickable entries which isn't ideal.

Note that we need to add a trim in here as otherwise newlines are being rendered and breaking our JSON file. We also need to make sure that we use {{- and -}} to trim any whitespace emitted from the tags.

As part of jvt.me#712.