Minor fixes

Four independent, minor changes (I can put them in different pull requests if preferred):
- Finish removing ModalController (without this, I had a blank window on load)
- Fix spelling of "filters"
- Use the principal on the command-line to get the HTTP/hostname ticket, for using Roost with backends besides roost-api.mit.edu (this is applicable to Roost 1.0 as well, but I wasn't sure if that was really still being developed)
- quote-reply in private conversations should stay private