Add messages in UnsupportedOperationExceptions thrown by iterator
Code style improvement
Add functions to check if an ID exists/is (in)valid
Added Search within date period

add search within date period with accompanying test
Code style fix

Renamed offsetIterator in InstanceIterator to follow the code style
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
Merge branch 'interface'
update_logic
Hotfix for path separator in Logic.java

Use File.separator to replace hard code to fix errors in r/w database on *nix systems
Merge branch 'master' of https://github.com/cs2103aug2014-w11-4j/main into update_logic

Conflicts:
	src/Logic.java
delete_Task tests added
delete_Update tests added
Refactor Task ToString
Integrated JournalController

Now support undo and redo functions
Integrated Executed Command

Allows logic to executed by reading the Command