Unify two body {} sections
Style tweaks

* WATCHMAN renders properly on Firefox now
* Fix a display bug when the page is short
* Leave a good amount of breathing room at the bottom of the page when
  there are lots of alerts
* Logical 3-column layout using flexbox
* Fewer elements, less nesting
* Some divs -> semantic tags
* Fewer styles, fewer hacks
* Less position: absolute
Env variable to turn off email sending

WATCHMAN_LOG_EMAILS_WITHOUT_SENDING
Doctring typo