Add actual implementations for Muon methods

Added implementations for:

• LHCb::Detector::Muon::FrontEndID (with unit tests)
• LHCb::Detector::Muon::ReadoutCond (with unit tests)

Also added

• example condition files for Muon chamber grids and readout conditions (needed in Boole)
• access to Muon ReadoutCond instances from DeMuon (see LHCb!3649 (merged))
• DeMuon unit tests (including access to example conditions)

Notes:

• includes !221 (merged) to avoid conflicts in the nightlies
• required by Boole!389 (merged)
• requires lhcb-conddb/lhcb-conditions-database!32 (merged)