Fix parsing original poster from page of posts.

We got it from a thread list no problem. But that isn't enough when following a
link to another thread, as we never see the list.
Fix dark mode for settings choice view.

This is the view when you tap a setting that has many choices, like which
YOSPOS theme you want.
Formatting.
Explanatory comment.
Update setting immediately from choices view.

This is when choosing e.g. a YOSPOS theme. Before it wouldn't take effect until
leaving the list of choices. This looks dumb on iPad, when you have the choice
screen open with a thread in behind.

The settings view now reloads on appear so it's up-to-date after the choice is
made.
Explain "keep sidebar open" setting.

Don't want anyone confused when it doesn't appear to immediately work. I
couldn't figure out how to consistently get UISplitViewController to relayout on
iOS 5 and iOS 6.
Add "Copy URL" action for links and browser.
Highlight mentions on word boundaries with /i.

Short usernames like "ev" would be highlighted unhelpfully and far too much, so
we search on word boundaries instead. And I found "pokeyman" would often be
written "Pokeyman", hence the case-insensitivity flag "i".
Update thread's bookmarked status in HTTP client.

We update everything else there. Might as well be consistent.
Show feedback when (un)bookmarking a thread.
Fade out closed threads' tag and rating.

Makes it more obvious that it's closed.

Fixes #147.
Thread cells' titles show two lines.

Three lines looks too cluttered, and doesn't show enough extra information to be
worthwhile on any threads I've come across.
Thread cell shows title right up to unread count.

The hardcoded 70 value seemed to be enough to show a five-digit unread count.
It's smarter not to hardcode this in case there's more unread posts in someone's
thread. Additionally, this shows more of a thread's title in the much more
frequent case that there are fewer than five digits' unread posts.