Added Date
Refactored output javadoc
Added parser to parse from string to a date object.
Refer to https://docs.google.com/spreadsheets/d/1A_enIhjFT220EPobggQ3lZ3hyz3evQ9SVA_b3iCm2ko/edit#gid=0
for the list of acceptable date formats

#40
Merge branch 'master' into parser/Victor
Executable
Output for Help
Added output for Exit
Output message for Errors
Merge remote-tracking branch 'origin/ui/victor' into controller/sharon
Added message field to Command Class
Merge branch 'ui/victor' into parser/Victor
Output for Undo
#61
Merge remote-tracking branch 'origin/parser/Victor' into controller/sharon
Merge remote-tracking branch 'origin/ui/victor' into controller/sharon
Major changes to controller flow

Checked for valid command type in resulting command and result classes returned by function calls to other components.
Organization and refactoring of code.
No longer uses Exception as program control flow.
[error] Still have errors, waiting for other components.