Implement Registry for Selection Factory

[calcuttj]

I have a plan to add a registry. For example like this

https://github.com/DUNE/protoduneana/blob/develop/protoduneana/Utilities/FitUtils/ThinSliceDriverRegistry.cxx

Then a new selection can be easily/more cleanly added as in
https://github.com/DUNE/protoduneana/blob/develop/protoduneana/Utilities/FitUtils/AbsCexDriver.cxx#L26

DECLARE_THINSLICEDRIVER_FACTORY_NS(protoana::AbsCexDriver, protoana, AbsCexDriver)

[sjgardiner]

Neat @calcuttj, looking forward to the PR!