Page: Use visibility:hidden instead of display:none to hide page

Avoiding display: none means we can calculate heights before transitions
This means less visual update after the end of the transition
and removes the need for binding to pageshow for page layout updates
this also has a small performance benefit since it avoids reflows

Closes gh-8241
Fixes gh-8137

css/structure/jquery.mobile.core.css

@@ -44,15 +44,15 @@ div.ui-mobile-viewport {
 	width: 100%;
 	min-height: 100%;
 	position: absolute;
-	display: none;
+	visibility: hidden;
 	border: 0;
 }
 /* On ios4, setting focus on the page element causes flashing during transitions when there is an outline, so we turn off outlines */
 .ui-page {
 	outline: none;
 }
 .ui-mobile .ui-page-active {
-	display: block;
+	visibility: visible;
 	overflow: visible;
 	overflow-x: hidden;
 }