RICH Photon Reco - More efficient mirror data cache update implementation.

Implements improvements to the method SIMDQuarticPhotonReco::MirrorData::update() which caches SIMD information when associated mirror pointers change. Main changes are :

• Avoid pointer dereferences, which are potentially slow due to cache issues, when they are not strictly required (i.e. pointer has not changed).
• Use private minimal implementations of Point, Vector and Plane that allow direct access to data members, that in turn allows MirrorData::update() to be a lot more efficient.

Relies on LHCb!1108 (merged)