Add "clear notifications" button, exclude posts from people who have blocked *you* from public/hashtag timelines

to only those from local users; Add link to "extended information" to
getting started in the UI; Add defaults for posting privacy; Change
how publish button looks depending on posting privacy chosen

Try to fix Travis CI setup

warning mentions preview into area where actual content would be

overshadow requirement for remote-lookup

untested, my vagrant is bugged again, submitted at gargron's request

Make the streaming API also handle websockets (because trying to get the browser EventSource interface to
work flawlessly was a nightmare). WARNING: This commit makes the web UI connect to the streaming API instead
of ActionCable like before. This means that if you are upgrading, you should set that up beforehand.

sounds complex, but really it just reorganizes the posting options and
adds a seperator line