PATCH: Preferences/Options dialog

Hi Dave,

Please find the patch adding support for the preferences/options dialog.
Initial patch was shared by Khushboo with me, but - I made some design
changes.

With this patch:
* Each preferences can be saved/retrieved per module basis.
* An object is created which represent that module in the preferences by
default.
* Module needs to override the register_preferences(...) method to register
certain preference.
* You can access other modules preference using static methods of the
preferences.
* A collection module (PGChildModule) will register show_node_<NODE_TYPE>,
and also refers the 'show_system_objects' in it, which can be accessed
using self.pref_show_system_objects, or can use class property
'show_system_obejcts', also there is one more property 'show_node', which
uses the 'pref_show_node' object of that module.

--

Thanks & Regards,

Ashesh Vashi
EnterpriseDB INDIA: Enterprise PostgreSQL Company
<http://www.enterprisedb.com>

*http://www.linkedin.com/in/asheshvashi*
<http://www.linkedin.com/in/asheshvashi>