getDate method now only supports limited number of date formats. Rejects the date before letting natty parse for relative dates if date format not supported
Refactored constants out from OptionalCommand Interpreter
Multiple input test cases done. Almost full coverage. Need to double check
Testing of boundary cases for isValidSelection method
Added new constants and made changes to the constant strings.
Merge pull request #69 from cs2103aug2014-t17-1j/Parser

Parser