Upgraded bootstrap to 3.3.4

src/UI/Content/Bootstrap/mixins/clearfix.less

@@ -0,0 +1,22 @@
+// Clearfix
+//
+// For modern browsers
+// 1. The space content is one way to avoid an Opera bug when the
+//    contenteditable attribute is included anywhere else in the document.
+//    Otherwise it causes space to appear at the top and bottom of elements
+//    that are clearfixed.
+// 2. The use of `table` rather than `block` is only necessary if using
+//    `:before` to contain the top-margins of child elements.
+//
+// Source: http://nicolasgallagher.com/micro-clearfix-hack/
+
+.clearfix() {
+  &:before,
+  &:after {
+    content: " "; // 1
+    display: table; // 2
+  }
+  &:after {
+    clear: both;
+  }
+}