Fixed some NetworkInventory issues

Tickets also expire on the clients side now.
Added extra error checking to ItemIDHolder

Will now check if Item objects have a null reference to their
itemObject GameObject.
Cleaned up LootTableScript

Got rid of excess code and unserialised m_itemList.
Start of NetworkInventory integration with shops

Currently they can only reset their inventory, GUI-based player
integration needs to be performed.
Updated scene shops with the NetworkInventory

Default inventory values can now be set but will be truncated if there
are more items than the capacity allows.