Widget styling with responsive horizontal and vertical centering

- New .widget style housing absolute positioning technique of horizontally and vertically centering
- Refactoring of .overlay class to be generic and override within .widget
- Applying .wrapper class to within .widget
Merge branch 'master' into chore/widget-single-column-layout
Styling for grouped sections of widget settings
Visual and Box changes to widget section styling

- Increased more margin bottom for section separation
- Decreased border radius
Keep overlay class within widget styling
Merge pull request #22 from Rise-Vision/chore/widget-single-column-layout

Widget single-column layout styling