Initial loading bar implementation
Initial loading bar implementation

See #726

Becomes visible when <body> has a class of `js-loading`

kevinansfield/Ghost-Admin,dbalders/Ghost-Admin,acburdine/Ghost-Admin,TryGhost/Ghost-Admin,acburdine/Ghost-Admin,TryGhost/Ghost-Admin,JohnONolan/Ghost-Admin,JohnONolan/Ghost-Admin,airycanon/Ghost-Admin,kevinansfield/Ghost-Admin,airycanon/Ghost-Admin,dbalders/Ghost-Admin