Test-Stub added
added tag{ident,name,timestamp}
added database persistence
added RESTfull-access via basepath/tags
removed superfluos jpa annotations
added
tag{ident,prepoint,pastpoint,timestamp,creation_timestamp,marked_as_deleted}
added database persistence
added RESTfull-access via basepath/expenses
added standard import for Serializable
changed ExpenseDAO:
- change insert:
	only insert non null values.
	if null value occurs let the db set the default.
	retreive the Entity after insert,
	because the DB-version could have changed.