Remove redundant SQLExceptions.

Histograms and Operators had SQLExceptions on their respective method
signatures which were not necessary at all.
Remove redundant print statements and methods.
Add special behaviour for natural key candidates.

If all possible values are known at runtime and the number of records is
less or equal than the number of distinct values, a
ClusteredValueProvider is used for Myriad in order to guarantee the
observed uniqueness.
Add lib directory for respective JDBC drivers.

Most JDBC Driver implementations (e.g., JDBC for DB2 or Oracle) are not
available as maven modules, are dependent on the exact database version,
and are not allowed to be shipped with any application.
Add Predicates utility class for JdbcConnector.