Implement findCommand to support conjunctive match for keywords, including dates. E.g. "find meeting march 31" only finds the tasks with meeting keyword and has a date of march 31.
Implement findCommand to support conjunctive match for keywords, including dates. E.g. "find meeting march 31" only finds the tasks with meeting keyword and has a date of march 31.

CS2103JAN2017-F14-B2/main,CS2103JAN2017-F14-B2/main,CS2103JAN2017-F14-B2/main