Added more tests for ReservationDao.
Added tests for DateConstraintRule.
Renamed InvalidArgumentsValidator -> Validator.
Renamed Argument -> Validatable.
Added tests for Validator.
Moved rules under their own package.
Changed pom.xml: updated junit to version 4.7.
Stripped useless comments in several places.
Created initial draft of DBConfig and moved db init code into it, unfinished, wip.