Cleanup State::Location implementation
- move Location into the namespace LHCb::Event::Enum::State and add a using statement to be backwards compatible
- use meta_enum to provide ADL-findable parse,toString,operator<< (which is the reason why the above is a dedicated namespace)
- use the above functionality in a number of location to reduce lines of code
Resolves #328 (closed)
Goes together with Rec!3667 (closed)