minor reflow of tree header

- remove absolutely positioned text (absolute text doesn't wrap correctly)
- associate hidden upload directly with 'click here' via span
- remove column split, rely on regular reflow

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

@@ -7999,14 +7999,15 @@ span#login_widget > .button .badge,
   margin: 0;
 }
 .alternate_upload input.fileinput {
-  background-color: red;
-  position: relative;
+  display: inline;
   opacity: 0;
   z-index: 2;
-  width: 295px;
-  margin-left: 163px;
-  cursor: pointer;
-  height: 26px;
+  width: 12ex;
+  margin-right: -12ex;
+}
+.alternate_upload .input-overlay {
+  display: inline-block;
+  font-weight: bold;
 }
 /**
  * Primary styles

IPython/html/static/tree/less/altuploadform.less

@@ -15,12 +15,14 @@
 
 .alternate_upload input.fileinput
 {
-    background-color:red;
-    position:relative;
+    display: inline;
     opacity: 0;
     z-index: 2;
-    width: 295px;
-    margin-left:163px;
-    cursor: pointer;
-    height: 26px;
+    width: 12ex;
+    margin-right: -12ex;
+}
+
+.alternate_upload .input-overlay {
+    display: inline-block;
+    font-weight: bold;
 }

IPython/html/templates/tree.html

@@ -34,15 +34,16 @@ data-terminals-available="{{terminals_available}}"
     <div class="tab-content">
     <div id="notebooks" class="tab-pane active">
         <div id="notebook_toolbar" class="row">
-            <div class="col-sm-8 no-padding">
-                <form id='alternate_upload'  class='alternate_upload' >
-                    <span id="notebook_list_info" style="position:absolute" >
-                        To import a notebook, drag the file onto the listing below or <strong>click here</strong>.
+            <div class="col-sm-12 no-padding">
+                <form id='alternate_upload'  class='alternate_upload'>
+                    <span id="notebook_list_info">
+                        To import a notebook, drag the file onto the listing below or
+                        <span class="input-overlay">
+                          <input type="file" name="datafile" class="fileinput" multiple='multiple'>
+                          click here.
+                        </span>
                     </span>
-                    <input type="file" name="datafile" class="fileinput" multiple='multiple'>
                 </form>
-            </div>
-            <div class="col-sm-4 no-padding tree-buttons">
               <span id="notebook_buttons" class="pull-right">
                 <div id="new-notebook-buttons" class="btn-group">
                   <button id="new_notebook" class="btn btn-default btn-xs">