Using rawElement function to generate a new html element for loading spinner.
This replaces the progress bar widget.
Bug: T161640
Change-Id: I949bce945def25de561c0ae0df971c3f609586ce
including:
- Using LESS for nested CSS
- Overrule `margin` of frameless OOUI `mw-revslider-toggle-button`
- Removing CSS that had no effect since some time
- Removing `!important` where not longer needed
Change-Id: I1ba01061ebafe799ca62dbb6ce5e79459612af23