Improve IE7/8 workarounds and remove IE6 ones

[zarino]

I just spotted a workaround for IE6 in position_map.js:

function position_map_box() {
    var $html = $('html');
    if ($html.hasClass('ie6')) {
        …
    } else {
        …
    }
}

And a quick search for ie6 in the *.scss files returns a surprising number of hits.

In the last 6 months (10th September–10th March), 19 people used IE6 to visit fixmystreet.com. That’s less than 0.01% of visitors.

Do we still need these workarounds?

[dracos]

Yes, I'd be happy to drop the IE6 things if also a little bit of work was put into improving IE7/8, only a few niggles but they're quite obvious (e.g. button background missing, navbar background missing, though the latter of those could be 'fixed' somewhat by #1350), and do have some thousands of sessions. Perhaps also checking which bits of IE7 workarounds are still needed (there's hardly any IE8 ones).