Fixed issue U4-5911 & part of U4-5101 - Allow descriptions on property editors to be localized

I was primarily fixing issue U4-5911 ( http://issues.umbraco.org/issue/U4-5911 )

However when looking through other tickets it seems this issue was also raised as part of U4-5101 ( http://issues.umbraco.org/issue/U4-5101 ), some of that ticket has a Pull request already, but it does not fix this issue.

- Updated the umbControlGroup directive so that the Description fields are now localized, for some reason only the label was being localized even though the text had been added to the UK English file.

- Updated the US English file so it includes the new Grid Localization text.
seems like a strange requirement since it should be the same without the 'description' part after the '@'