refactored callAdd() method for Parser
Merge pull request #63 from cs2103aug2014-w15-3J/Logic

Merge Master with Logic
Added Exception to Event Constructor
Redesigned Undo and Redo Methods
Added equals() method to Task, Date and Time class
Added *.json into gitignore

To prevent the commit of database file to repository
implemented untick() and uncmi()
Merge branch 'parser'
comment off the part related to logic, focus on UI appearance first
Merge remote-tracking branch 'origin/master'
FIxed the constructor bug in Logic

Wrong constructor called for Event
Merge pull request #64 from cs2103aug2014-w15-3J/master

Merge Logic with Master