[2.0] DDC-169 - Finalized implementation of Schema diff algorithm, added diffs of sequences and foreign keys. Fixed several bugs and changed the API of the Schema objects.

[2.0] - DDC-169 - Began refactoring of DBAL code, introduced object notation for a database schema, including Tables, Indexes, Constraints, Sequences and Columns. Added a CreateSql Visitor which transforms a schema object graph into the required SQL statements to create it. Next: Replacing SchemaTool::getCreateSql() with new syntax...