Adopt theming system of Angular Material

The SASS has been simplified so that different themes can be applied by
only using the $mdThemingProvider serivce.

The resulting design is more "Materialized" and less prone to the
future changes of Angular Material.

UI/WebServerResources/scss/components/card/card-theme.scss

@@ -0,0 +1,5 @@
+md-card {
+  &.md-default-theme {
+    background-color: sg-color($sogoPaper, 50);
+  }
+}

UI/WebServerResources/scss/components/card/card.scss

@@ -8,10 +8,6 @@ md-card {
     transition: $swift-ease-in-out;
   }
 
-  &.md-default-theme {
-    background-color: sg-color($sogoPaper, 50);
-  }
-
   // Collapsed/expanded states for cards in ACL editor
   &.sg-collapsed, &.sg-expanded {
     transition: $swift-ease-in-out;