API Move state to enwtine properties, provide API for preview.

Also the preview state is now kept between panel loads. We also use a
redraw function to update appearance based on the state.

admin/code/LeftAndMain.php

@@ -1044,7 +1044,7 @@ public function getEditForm($id = null, $fields = null) {
 				$fields->push(new HiddenField('ParentID'));
 			}
 
-			// Added in-line to the form, but plucked into different view by LeftAndMain.Preview.js upon load
+			// Added in-line to the form, but plucked into different view by frontend scripts.
 			if(in_array('CMSPreviewable', class_implements($record))) {
 				$navField = new LiteralField('SilverStripeNavigator', $this->getSilverStripeNavigator());
 				$navField->setAllowHTML(true);

admin/javascript/LeftAndMain.EditForm.js

@@ -94,14 +94,6 @@
 					$('.cms-container').clearCurrentTabState(); // clear state to avoid override later on
 					firstTabWithErrors.closest('.tabset').tabs('select', firstTabWithErrors.attr('id'));
 				}
-
-				// Move navigator to preview if one is available.
-				// If not, just leave the links in the form.
-				var previewEl = $('.cms-preview');
-				if(previewEl.length) {
-					// TODO Relies on DOM element order (the second .cms-navigator is the "old" one)
-					previewEl.find('.cms-preview-controls').html(this.find('.cms-navigator').detach());
-				}
 
 				this._super();
 			},