Set up pipeline as a separate package

[SamuelBrand1]

At the moment AnalysisPipeline pakage/env (soon to be renamed EpiAwarePipeline as per #230 ) has a combination of generic functions and abstract types and some specific behaviours (e.g. dispatching on prior predictive modelling with RtwithoutRenewalPriorPipeline).

It would be neater to abstract the pipeline infrastructure into a full package which can be used by the specific pipeline src code.

Tasks

• Move generic EpiAwarePipeline tools into a package hosts at ~/EpiAwarePipeline. #280
• Do Work out how to use @testitem in pipeline #206
• Do Setup CI for analysis pipeline #209