Hibernate Configuration File (cfg.xml) Wizard: add possibility to import existing DTP connection settings

https://issues.jboss.org/browse/JBIDE-1420 - initial idea of this enhancement.
I see 2 ways to implement the feature:
1) add "Import DTP connection" button -> small dialog just with combobox - to select one existing DTP connection and Ok & Cancel buttons;
2) add checkbox "Import DTP connection" and combobox - to select one existing DTP connection - here to import DTP connection is necessary to check "Import DTP connection" and select connection from combobox, if the user change some config value - checkbox should become unchecked and empty valu in combobox be selected