Update H2 to current version and create SQL-92 join clauses

- updated H2 to current version 1.4.177, the old version throws an SQL error when dropping (former) foreign key columns
- replaced implementation of assembleSelectStatementWithAttributes() with code from PostgresqlExpression that generates SQL-92 compatible join clauses, making left outer joins work
- added catch clause for an IllegalArgumentException that occurred when no sequence existed yet