OAuth2: Fix app icon uploading

- App icon changing is on an SSL page, so it should set
 an icon_url with https
- Use a unique name based on contents, to avoid CDN caching
 issues
OAuth2: Save http links to client.icon_url
Consistently use CSS prefixes

When browsers first introduce support for new CSS features, they often do so
with a *vendor prefix* - `-moz-` for Firefox, `-webkit-` for Chrome and Safari,
`-ms-` for IE.  It's annoying to deal with all of these, so we've written a few
Less functions to help.

Unfortunately, we haven't consistently used them.  This is most evident in how
the search box looks wonky to people using older versions of Firefox, because I
didn't use the `-moz-` prefix to `box-sizing`.

From a quick search, it looks like the only two functions we didn't use all the
time are `.transition` and `.box-sizing`; this should change all un-functioned
instances over.  This shouldn't affect a huge percentage of users, but it's
easy enough to do.

* http://caniuse.com/#search=transition
* http://caniuse.com/#search=box-sizing

Fixes #1146.
Search box: adjust tabindex

Adding a search submit button affected the tabbing behavior in the search box -
namely, it now began to take two tabs, rather than one, to get to the "limit my
search to /r/whatever" when on a subreddit page.

This changes add an explicit ordering: search text -> limit my search -> submit
button.  While this adds an extra tab to get to the submit button, that's not
really necessary, as pressing enter anywhere on the form also submits it.

There are many elements on the page with tabindices defined.  However, with the
exception of the "jump to content" link, they seem fairly random, so I'm not
terribly concerned about adjusted the overall index of the search form (that
is, how many tabs it takes to get to it from a freshly-loaded page).  It is
roughly in the same place as before - far enough down no one will want to tab
all the way to it. :)
Merge pull request #2 from reddit/master

Catch-Up #2