[2.0][DDC-459] Moved Doctrine\ORM\AbstractQuery to Doctrine\ORM\Query\AbstractQuery, which is compatible with Doctrine Coding Standards

DDC-126 - Make Query, NativeQuery Fluent-Interfaces for all their set Methods, renamed setExpireQueryCache() and setExpireResultCache() to expireQueryCache() and expireResultCache(). Updated UPGRADE_TO_2_0 document accordingly.

[2.0] Moved code between Query and AbstractQuery. Added first NativeQuery implementation. Hydration work and code movements for discriminator column usage. Started implementing Single Table Inheritance.