Adding query builder interface and PDO implementation of it

* This will allow the system to generate queries in different persistence backends, like PDO (example implementation) and any other that seems more likely in the future.

Change-Id: I0d101a8da4116f92074f9ab5bd2de0e6b64af0fb
Adding repository interface and PDO implementation of it

* This will allow the system to have queries' repositories in different persistence backends, like PDO (example implementation) and any other that seems more likely in the future.

Change-Id: I8df5e24ce51c17d573e61e637a51d6e81e35d62c
Adding support guy repository + design improvements

* Persistence namespace added, all namespaces related placed inside
* Moving AbstractPdoRepository to PdoPersistenceAdapter, which makes more sense for persistence agnostic Repositories

Change-Id: I8cf368d0145bd2cee10cdde85c14ea0e9e07d87b