Update SQLServerPlatform.php by adding methods related to schema.

The platform indicates support for schema's here: https://github.com/doctrine/dbal/blob/master/lib/Doctrine/DBAL/Platforms/SQLServerPlatform.php#L129

But is missing relevant methods:
schemaNeedsCreation() --> to detect if schema creation is needed
and
getCreateSchemaSQL() --> to create a schema