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/
```
Maybe a simpler approach would be to wrap those things in `block`s that can be overridden to be empty? (Something I suggested in the template updates in [cfgov-sheer-templates](https://github.com/cfpb/cfgov-sheer-templates/blob/master/_layouts/base.html) that we never rolled out to our project.)