Add User Creator, Validator for input Data for RegistrationServlet 
Add error404 page
Change registration servlet and jsp files
registration successed
Merge remote-tracking branch 'origin/master' into aleg

Conflicts:
	BuyIt/WebApp/WEB-INF/web.xml
	BuyIt/WebApp/jsp/registration.jsp
	
Login Servlet
login
Merge chemodurov branch with Alegos.
Create category_viewer.jsp, item_preview.jsp and CategoryServlet