studio - revises z-index/element depth levels for modals, notifications,…

studio - revises z-index/element depth levels for modals, notifications, prompts, and alerts to use universal .depth Sass extends

cms/static/sass/elements/_modal.scss

@@ -2,22 +2,22 @@
 // ====================
 
 .modal-cover {
+	@extend .depth3;
 	display: none;
 	position: fixed;
 	top: 0;
 	left: 0;
-	z-index: 1000;
 	width: 100%;
 	height: 100%;
 	background: rgba(0, 0, 0, .8);
 }
 
 .modal {
+	@extend .depth4;
 	display: none;
 	position: fixed;
 	top: 60px;
 	left: 50%;
-	z-index: 1001;
 	width: 930px;
 	height: 540px;
 	margin-left: -465px;
@@ -61,12 +61,12 @@
 
 // lean modal alternative
 #lean_overlay {
+	@extend .depth4;
 	position: fixed;
-	z-index: 10000;
 	top: 0px;
 	left: 0px;
 	display: none;
 	height: 100%;
 	width: 100%;
 	background: $black;
-}
+}
\ No newline at end of file

cms/static/sass/elements/_system-feedback.scss

@@ -144,7 +144,7 @@
 
 // prompts
 .wrapper-prompt {
-  @extend .depth4;
+  @extend .depth5;
   @include transition(all 0.05s ease-in-out);
   position: fixed;
   top: 0;
@@ -242,7 +242,7 @@
 
 // notifications
 .wrapper-notification {
-  @extend .depth3;
+  @extend .depth5;
   @include clearfix();
   @include box-shadow(0 -1px 3px $shadow, inset 0 3px 1px $blue);
   position: fixed;