Fixed the instantiation of the page element in the session
Removed the dependency on the session in ElementNotFoundException

This removes the last usage of the session inside elements.
Changed the constructor arguments of the elements to their dependencies

The constructor now receives the driver and the selectors handler instead
of the session.
Decoupled the DriverInterface from the NodeElement

This avoids a circular dependency. The driver interface now returns an
array of XPath for found elements, and Element::find() instantiates the
NodeElement for them.
The driver is now the low level API which does not depend on any other
part of Mink (but used by other parts).