Add a function to consolidate and tidy raw BCEA data tables

From discussion:

...consider some naming conventions for these type of functions. That way if/when those get spun off into a separate package, they still make sense. The verb_noun combo works well but I don't know if tidy quite fits? join_bcea? consolidate_bcea? merge_bcea? fuse_bcea? pool_bcea? integrate_bcea?

Start by locating the raw BCEA data tables and the package code that currently handles them; the issue does not name files or tests. Clarify the intended consolidation and tidying behavior and choose a verb_noun function name from the discussion. Done means the agreed function exists with documented behavior and coverage for the resulting tables.

Written by the indexing model from the issue text.