Websockets: add metrics for connection time and failures.

This should hopefully give us better insight into how sutro's holding up
from the client perspective and potentially allow for earlier alerting
on failures.
Pad submit buttons

I noticed that in Chrome, some of our buttons had no padding at all, which made
them look terrible.  Others, however, were fine.  This turned out to be a
different between `<input type="submit">` and `<button>` elements.  The easiest
place to see this was comparing the save buttons on `/prefs` (ugly) and any of
the other preferences tabs (pretty).

In `reddit.less`, we reset the margin and padding of a whole bunch of elements
to be 0.  `<input>`s are in this list, although `<button>`s are not.\*  Thus,
no padding.

Now we set the padding `<button>`s and select types of `<input>`s.  I chose the
rules from what Chrome automatically applies, since that seemed like a
reasonable default.

Firefox notably ignored the `padding: 0` before, and continues to ignore
whatever I set, with the result that it looked good before and still looks
good now.  Whatever.

----

\* I decided not to add a reset of button margin and padding.  Padding we now
set again to something useful, per this commit, but margin could have effects
across the site that I didn't want to track down.
Whitelist publicly-visible attributes on private subreddits

This plugs a hole where you could get the number of subscribers
of a private subreddit. Thanks to /u/GoldenSights for the report

Previously a blacklist was used to drop private attrs,
but a whitelist is less likely to result in info leakage when
new attributes are added.
Handle backslash trickery in VDestination