Make VPTrackingInfo available outside of PrPixel

Right now, relevant pixel-detector information is obtained through the VPTrackingInfo object, which interprets the EventContext.

The cheating pattern recognitions, which live in PrMCTools, should also be able to access this information. This can be solved by changing PrPixel from a Gaudi module to a Gaudi library in the CMakeLists. Other solutions are also welcome.