Improvements to scalar adapters typing.

[minox86]

1. Every scalar adapter should be optional, even for custom scalars. The default should be an identityAdapter.
2. When a user define a scalar adapter he should have the ability set only a part of the adapter and other methods fallback to identityAdapter.
3. Exactly as datasources, scalar adapters should have mongo/sql params only if the the DAOContext has mongo/sql data sources. When there's no entity with a driver the DAOContext should not receive configurations for that driver.
4. If the ID scalar is configured to be generated by the user, its scalar adapter should be required and the generate method should be also required.

[edobrb]

Number 4 is not possible since the generator can be specified directly in the overrides of a specific DAO.
A runtime error should be enough for number 4.

[minox86]

Well, we can go on without the 4.