Added Exit CommandType
Added switch case for parsing of each Command Type
Added hasOption(OptionType) method
Added add List<Option> to options
Added parseDate
Refactored CommandAdd
Addded constant for Priority
Tested after refactoring CommandAdd
Fixed toString method
Added trim() to each item
Added parseDelete
Added parseList
Added parseUndo and parseRedo
Added parseSearch
Added PRIORITY_NONE constant
Fixed how to retrieve Command
Editted to work with new method
Added parseUpdate
Added parseDate
Changed way to call execution of commands