Bring dashboard width in line with limelight

It's not nice having yet another wrapper around all the wrappers,
but I can't see a nicer way and this is consistent with our
other big app.
Style tagline identically to current dashboards
Style modules with the same margins as limelight

The application of the group class makes use of govuk_template
styles in _basic.scss commented as "self clearing floats".
Add Stagecraft stub text for FCO Pingdom
Fix more info callout width on small screens
Add 'more info' copy for availability single module
Merge pull request #36 from alphagov/style-tweaks

Style tweaks