Library: enable Material Design ui elements

A new .scss file is added to library

src/20.x/morpheus-master/sass/base/_material-defaults.scss

This file contains the following boolean variables, which when set to true will change that particular ui element from the current Morpheus design to a more Google Material one.

$standard-spacing-as-material
$sites-nav-as-material
$portal-as-material
$tool-menu-as-material
$buttons-as-material
$top-header-as-material
$cards-as-material
$lessons-as-material

The attached screenshots correlate to the variables being enabled. In the pull request, I set all the variables as false. I'd like the community to weigh in on whether any should be set to true for the out of the box 20.0 skin.

If you do not wish to enable these in your sakai instance, set the variables to false in

src/20.x/morpheus-master/sass/base/_material-defaults.scss

or in your skin's _customization.scss file.