Responsive fixes

- Make composer absolutely positioned on mobile to work around iOS 8/9
bug
- Make search results dropdown appear on mobile

closes flarum/core#137

less/lib/Search.less

@@ -1,3 +1,6 @@
+.Search {
+  position: relative;
+}
 @media @tablet-up {
   .Search {
     input:focus, &.active input, .Search-results {
@@ -11,6 +14,10 @@
   left: auto;
   right: 0;
 
+  @media @phone {
+    left: 0;
+  }
+
   > li > a {
     white-space: normal;
   }