Added Stock.java and StockType.java and let Album and Song implements it
such that it is possible to group 2 types of object in 1 list.
Added Cart.java to store the stocks a user has selected to buy.
Deleted duplicate Cart.java
Changed names of the checkboxes in the search results.
Changed name of the 'Add to Cart' button.
Change name 'getStocks()' to 'getItems()' in Cart.java.
Changed session in welcome.jsp to link to Cart.java.
Moved XML into WebContent/WEB-INF. Added the schema for validation.
noResult.jsp: Modified footer due to earlier rename.
results.jsp: Removed the searchFooter to move submit button to be inside
the same form as the checkboxes.
Added validation for XML file using the XSD file.