issue #22 add Workshift.java, WorkshiftDao.java, WorkshiftDaoImpl.java, WorkshiftDaoImplTest.java
issue #22 closedAt of Workshift

add to db not default closedAt
add class helper in tests
test closedAt set db
test closedAt reading from db
test openedAt notNull
issue #22 DaySum

DaySum is BigDecimal
test DaySum add to db
test DaySum reading from db