[Frontend] CSS and markup for iframe

WTD-1150
WTD-1145
CSS and markup to cause iframes to layout properly without double scroll bars

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

@@ -40,3 +40,4 @@
 @import "helpers/wait-spinner";
 @import "properties";
 @import "autoflow";
+@import "iframe";