Adding Schema Support

This commit adds schema support to Simple.Data.Ado providers via the new
ISchemaConnectionProvider interface, and allows them to support a schema
per instance of Database.Open(...).  This is primarily used for Oracle
databases.  In order to use the schema, just add the schema name to the
appropriate Database.Open call (e.g.
Database.OpenNamedConnection("TestConnectionName", "TEST_SCHEMA_NAME")
).