Add messages in UnsupportedOperationExceptions thrown by iterator
Add JournalController class to support undo/redo actions
Fix Conflict in Logic Checkout
Code style improvement
Add functions to check if an ID exists/is (in)valid
Code style fix

Renamed offsetIterator in InstanceIterator to follow the code style
Resolve Conflict in LogicTest
Add description for action to be returned when undo/redo
resolve conflict in Logic Class
Let JournalManager support generics like DatabaseManager
Add methods to get size of stacks
Add tests for JournalManager
Merge branch 'master' into journal
Clean up JournalControllerTest
Merge branch 'dbmanager'
Created interface code skeleton and linkage
Created Command and CommandType classes
Merge branch 'interface'
Major changes to Command class

The command class now contains all variables for every type of command.
Only the required variables will be initialised and become valid for
usage based on command type.
Completed parsing for Search, Delete