Track page views

Tracks viewing of confidential or privileged information, and adds it to the feed of database changes.

Requires config:
```
[[tracking]]
page_viewed = "Page Viewed"
```
Incidentally, since this is a decorator you're just applying manually, next year when we do this for realsies, I can walk you through writing decorators which themselves take arguments.  So like you could say ``@log_pageview(Attendee)`` or ``@log_pageview(Group)`` or ``@log_pageview('budget')`` and then not need so many if-statements within the implementation.