Rich update with additional detector element access classes

This contains the remaining DeXX classes for Rich mirrors, PMTs in Rich1 and Rich2.

Also contains an overhaul of the classes, developed with the reconstruction for better support there.

1. Introduce a number of base classes for shared generic functionality. Greatly simplifies the implementation in a number of places (e.g. the mirrors where there are four types, but now most of the functionality is in a single place). Also aids in the reconstruction downstream where having a single type that each entity can be access via is very useful.

2. A general clean up / modernization of the code.

3. Improvements to some static generator methods, which where not thread safe and also leaked memory on shutdown because the global static entities were never deleted.