Add date and time constraints (start <= end)
Add unit tests for calendar events' constraints
Add calendar events' unit tests as test suites
Add a utility class for unrelated functions
Add unit tests for isNullOrWhitespace(String)
Add utility unit tests as unit test suites
Use isNullOrWhitespace as a title setter check

This solves some unit tests (notably, those with special
characters and whitespace) failing.