Import missing ApplicationException class (#332)

When attempting to add database columns when the table does not exist, an ApplicationException is thrown but the class is not imported. This quick fix resolves the issue.

Author: LarryBarker

classes/ModelModel.php

@@ -1,6 +1,7 @@
 <?php namespace RainLab\Builder\Classes;
 
 use DirectoryIterator;
+use ApplicationException;
 use SystemException;
 use Validator;
 use Lang;