Set min-height for header/footer element

Fixes height issue on these elements when the screen height is very small
e.g. when using a phone keyboard appears

skins/elastic/styles/layout.less

@@ -137,6 +137,7 @@ body > #layout {
             font-weight: bold;
             line-height: @layout-header-height;
             height: @layout-header-height;
+            min-height: @layout-header-height;
             padding: 0 .25em;
             margin: 0;
             position: relative; /* for absolute positioning of searchbar */