fix(legal): fix rendering of legal pages when loaded directly via url

I refactored the template fetching so that we can use it from the route handler when rendering pages dynamically and from the grunt task when generating pages statically.

Fixes #1372.

@shane-tomlinson r?
Yeah, the legal templates are sourced from the legal repo, so we convert them markdown to HTML and put it in the template destination directory, at which point they are finished with processing. We're using them here to help process the other page templates. I'll add a note!