Committed new ProductPanel

Added new implementation of ProductPanel to project. Updated list
population bahaviour to reflect modifications in CustomerPanel. Need to
fix new/edit/delete bahaviours to reflect modifications in
CustomerPanel. Uncommented call to productPanel.updateUser(user) in
RetailSystemSwingView.
Overrode equals method.

Products are now compared for equivalence based on their id.
Fixed supplier combobox bug

Supplier combobox was not setting to the correct supplier when entering
edit mode. Added supplierBox.setSelectedObject(s) to list selection
listener, also overrode Supplier.equals() to ensure suppliers were being
compared on their ids for their equivalence, as opposed to
direct/default object comparison.
Merge branch 'master' into eoin