Implement exit commnad
parseCommand returns command object
Merge branch 'wd-parser'
Fix Controller
Checks whether user input contains only one command word
command details is an empty string if user input contains only the command
Add assertion to ensure commandDetails is not empty
Implement parsing of undo command
Add getter and setter for task ids to complete
Import mentaregex matches
Implement parsing of complete command
No point having a static method here
Factor out date parsing
Implement list command
Add searchDate field to command class
Add searchStartDate field to command class
Add searchEndDate field to command class
Return the command object to controller

command is invalid if getCommandType return INVALID
Check for invalid command type instead of checking for null object
Add getter and setter for searchEndDate