Fix bugs around operations happening between modes

The `release` method is meant to clean up a sticky
element before removal from the store.

The part of this that cleared CSS added due to
being in dialog mode was only run if still in that
mode.

In the template folder JS, we set the mode before
running `recalculate` so elements can be cleaned
in a different mode to that they were last in.
This meant some CSS wasn't being cleaned up.

This sometimes caused an effect where elements
that were added back to the DOM but not stuck
would still have CSS used when they were last
stuck.

This commit also includes the addition of some
missing code that adds back CSS to offset an
element when in a dialog stack.

app/assets/javascripts/stick-to-window-when-scrolling.js

@@ -576,9 +576,8 @@
 
       el.removeStickyClasses(this);
       $el.css('width', '');
-      if (_mode === 'dialog') {
-        dialog.releaseEl(el, this);
-      }
+      // clear styles from any elements stuck while in a dialog mode
+      dialog.releaseEl(el, this);
       el.removeShim();
       el.release(this);
     }
@@ -658,9 +657,15 @@
     }
   };
   stickAtTop.unstop = function (el) {
+    var offset = 0;
+
+    if (_mode === 'dialog') {
+      offset = dialog.getOffsetFromEdge(el, this);
+    }
+
     el.$fixedEl.css({
       'position': '',
-      'top': ''
+      'top': offset + 'px'
     });
     el.unstop();
   };