Added database generator to compare different source database with its target database.

1. Added comparatorClass attribute in sku-conf
2. Add method createDatabaseComparator(databaseName) in
DbOperatorFactory interface.
3. Added getDatabaseComparatorClass(databaseName) in
DbConfigurationManagement class.
4. Added createDatabaseComparator(databaseName) in DbOperatorFactoryImpl
5. Added SchemaMetaDataComparator interface and
MySQLSchemaMetaDataComparatorImpl.