[view/data-explorer][m]: (refs #14) introduce ability to change number of rows viewed.

* This also necessitated a nice refactor whereby DataExplorer subviews running off a common Backbone Collection (DocumentList) re-rendering themselves in response to changes in that Collection.

demo/style/style.css

@@ -239,3 +239,13 @@ span.tooltip-status {
   right: 0px;
   background: white;
 }
+
+.nav-pagination {
+  display: inline;
+  float: right;
+  list-style-type: none;
+}
+
+.nav-pagination input {
+  width: 40px;
+}