Don't select all editor text on render in admin

ACE editor selects all text on setValue by default unless a cursor
position is passed as second param. This patch positions the cursor at
the beginning of the document instead.

Author: aitorciki

martor/static/martor/js/martor.js

@@ -831,7 +831,7 @@
 
             // Set initial value if has the content before.
             if (textareaId.val() != '') {
-                editor.setValue(textareaId.val());
+                editor.setValue(textareaId.val(), -1);
             }
         });// end each `mainMartor`
 };