Truth matching with dynamically created relation tables

Currently, the MCTruthAndBkgCat python class assumes that Relations tables are read from file. This MR allows the user to create a relations table and pass it to the class.

Use-case: truth-matching of candidates that are built on the fly, e.g. the raw event.

Part of the set: !4266 (merged) Moore!4434 (merged) DaVinci!1248 (merged) lhcb-datapkg/PRConfig!527 (merged)