Implemented querying and moving of user inventory

- Updated documentation to be current on all classes
- Added support for querying a user’s inventory
- Added support for performing actions on a query result (i.e moving
resulting items to the shop)
- Implemented base class for query results (ItemList)
- Modified dict-like and list-like classes to inherit UserDict instead
of overriding functions
- Fixed bug in HTMLForm which was not grabbing ‘select’ inputs
- Fixed bug with parsed item details not being returned as strings