Adapter capability

[GerkinDev]

In order to help the user, the next adapter structure should allow developer to indicate which features are available, such as query operator, schemas, or pubsub (see #5). It may require each query operator to be casted using its own function.

Maybe a QL translator class may help, to translate from Diaspora QL & DB specific language.

But there are still some exceptions: Some adapters (such as In Memory, LocalStorage or WebAPI) should not translate query language from objects to string or objects. WebAPI should transfert the query "as is" and InMemory or LocalStorage may generate a matcher function to perform the query. The next adapters structure should support that