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"
```
Considering that Anthrocon is a nonprofit and publishes their profits and losses and such, I'm surprised that they would feel like this aggregate data needs to be so tightly restricted.  On the other hand, more logging is more better.