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