More rigorous input handling for schedule

[fymbc]

When inputting add command add n/John Doe p/98765432 e/[email protected] a/John street, block 123, #01-01 t/Tuesday-1300- 1500 s/economics r/50.00 paid/100.00 owed/0.00, the whitespace in schedule format throws an error.

While constraint is specified in the error message, it is not outright specified in the UG. I suggest for the team to either state it in the UG or (recommend) to allow for more rigorous input handling to allow for whitespace as fast typists may accidentally input a whitespace.