Refresh timelines when streaming API reconnects in the UI

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

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

they have been loaded and favourited/reblogged from another source

Since the status JSON returned from public/hashtag streams does not
contain favourited/reblogged attributes, merging them should not
override existing ones.

FanOutOnWriteService. The only recipient-specific part on them
is reblogged/favourited. But since only newly created statuses
appear on them, it is safe to assume that both attributes would
be false

redis-backed "mentions" timeline as redundant (given notifications)

Changing the way the background image is positioned and the box is sized should fix problems with the text overlapping the image on mobile browsers and Edge.

nested inside a common parent (<Account>), instead they all embed <HeaderContainer />

the public timeline has been using