Rewrite Ghost Objects to only rely on property lazy loading

[Ocramius]

The current approach of ghost objects is to lazy-load the object when the public API of the object is hit.

This involves that a lot of logic is under-optimized and can cause lazy-initialization even when not needed (for example, when accessing API that doesn't fetch internal object state, or that doesn't rely on the object's lazyness).

To mitigate that, public API lazy loading shall be completely removed, replaced by lazy properties only.

This way, compatibilizing ProxyManager with Doctrine 2 ORM will be easy and effortless.

[Ocramius]

Depends on PHP 5.4

[Ocramius]

Handled in #159 and #192