Use better clustered indexes on SQL Server

SQL Server uses a clustered index to defined how the data is organized physically on disk.

By default in Nuxeo we don't define a clustered index, so the primary key (for tables with one) is used, however this primary key is a random UUID which means that data keeps getting reorganized on disk on practically every insert or delete.

Change this to use a synthetic IDENTITY column (which we'll name _oid) which will be used just for the purpose of adding a clustered index on it.

Also provide a migration script for existing databases.