Update UserWebService
Update category_viewer.jsp, item_preview.jsp, CategoryServlet
Merge remote-tracking branch 'origin/aleg' into chemodurov

Conflicts:
	BuyIt/WebApp/WEB-INF/web.xml
Create registration form javascript validator.
Change logo
Merge remote-tracking branch 'origin/aleg' into chemodurov

Conflicts:
	BuyIt/WebApp/jsp/registration.jsp
Add modal popup windows to item-preview.jsp
Update item_preview.jsp and item_preview.css. Add mock images.