Build: Add more tested browsers, update existing ones

Firefox: I added 3.6 and last two ESRs. Firefox 3.0 errors with `Some of your tests did a full page reload`. Do we want to keep supporting 3.0? We'll need to fix sth if we do; otherwise, Firefox 3.6 is old enough. Firefox 29 consistently disconnects, if it starts at all, it stops at 23/35 so I couldn't update the version here. Any ideas? Can it be our bug?

Chrome: 4.0 doesn't even exist in BrowserStack, the oldest available is 14. Is it enough? Would it be OK to bump minimal supported version to it? I added v24 as well since it shares v8 version with Node 0.10.

Safari: Added 4.0, 5.0, 5.1 & 6.0. Removed 6.1 since it shares the same engine version with 7.0 and we're already testing *a lot*. I know @markelog was opposed to removing in case they start differing but I don't think we should guard ourselves so much about such potential stupidity on WebKit part, especially that we don't test all 26 supported Firefox versions etc. and we already have a lot of browsers. If the rest of you feel similarly to @markelog, I'll bring 6.1 back.

Opera: tried 11.6, 12.0 & 12.6 but it still doesn't connect. @markelog, did you contact BrowserStack about it? Did they reply?

iOS: Added 5.1 to current 6.0 & 7.0.

Android: Added 4.0 & 4.2 to current 2.3 & 4.1.