Leadership calendar PDF

Still needs style tweaks to the PDF but figured I can tackle that next sprint.
Also this needs the following ENV vars set:

```
PDF_URL_RULE_1=/the-bureau/leadership-calendar/pdf/
PDF_RENDER_URL_1=DEMO-DOMAIN/the-bureau/leadership-calendar/print/
```
I'd like to suggest the addition of something to this comment: A list of places where someone can see examples of this filter being used.