Review SCSS refactoring for to-be-deprecated Bourbon functions (#1959)

* [Frontend] Refactor SCSS to remove deprecated @includes

Fixes #1891
- In progress

* [Frontend] Refactor SCSS to remove deprecated @includes

Fixes #1891
Making bourbon happy by refactoring to-be-deprecated
calls to prefixing @includes:
- transform and related CSS;
- flex and related CSS;
- Fixed double semi-colons to single;

platform/commonUI/general/res/sass/_mixins.scss

@@ -382,7 +382,7 @@
     /* This doesn't work on an element inside an element with absolute positioning that has height: auto */
     //position: relative;
     top: 50%;
-    @include transform(translateY(-50%));
+    transform: translateY(-50%);
 }
 
 @mixin verticalCenterBlock($holderH, $itemH) {