Smooth notebook scrolling on pager closing.

avoid brutal jump of notebook on closing pager, when notebook is scroll
to max

IPython/html/static/notebook/less/notebook.less

@@ -70,6 +70,7 p {
 
 .end_space {
     min-height: 100px;
+    transition: height .2s ease;
 }
 
 .notebook_app #header {

IPython/html/static/style/style.min.css

@@ -10097,6 +10097,7 p {
 }
 .end_space {
   min-height: 100px;
+  transition: height .2s ease;
 }
 .notebook_app #header {
   -webkit-box-shadow: 0px 0px 12px 1px rgba(87, 87, 87, 0.2);