Automatically generate projections from DbEntities

[agoulti]

In ReadOnly transactions we don't need the full DbEntities. Simple data classes that carry the same data will do.
Also, with flat projections we can do optimizations, such as doing multiple targeted database queries instead of an eager join.

It would make things easier if Yawn could automatically generate these projections from DbEntities, reducing duplication.

Ideally: for a DbEntity it would automatically generate a class (DbEntityProjection? ) that would contain exactly the column fields from the original entity (but not anything that references other tables or requires join/lazy fetch)