Use some HTTPSFuture in CampfireBot

Summary:
  - Use PhutilURI to correct for specifying "https://yourname.campfire.com/" instead of "https://yourname.campfire.com".
  - Use HTTPSFuture to get logging via `--trace` and error detection (CA stuff should be OK since 37signals has real certs).
  - On destruction, only try to leave rooms we've actually joined.

Test Plan: Setup a bot, had it join a room, talked to it.

Reviewers: indiefan

Reviewed By: indiefan

CC: aran

Differential Revision: https://secure.phabricator.com/D4849