Fix for progressbar styling

Modified the styling for the progressbar as the last fix didn't seem to
work in latest updates of Chrome, where the progressbar in Umbraco 7.1.6 and Chrome Version 37.0.2062.103 m hadn't a full width.

Previously pull requests: https://github.com/umbraco/Umbraco-CMS/pull/420 and https://github.com/umbraco/Umbraco-CMS/pull/456
Yes, I agree that inline styling should be avoid as possible. I have also tried to define the progressbar with a simular markup and moved the styling to umb-loader-wrapper.