Prevent env indicator from occasionally wrapping

Occasionally the browser would render the environment indicator on a
new line. A refresh would sometimes fix, sometimes not even though the
code was unchanged.

* Attempt to fix by removing floats and float calculations
* Mark indicator as inline-block and include inline-block IE7 hack
* Reposition crown background in IE7
Tweak vertical-alignment of app title and label

Without a vertical alignment set different fonts (eg Arial on Windows)
line up less nicely.
Hide environment label on small widths

Label is an enhancement, it repeats what’s in the domain part of the
URL, which is more obvious on mobile. Prevents wrapping.
Merge pull request #54 from alphagov/env-label-position-fix

Prevent environment indicator from occasionally wrapping