added strings for LHC modes
requested to merge github/fork/andreh12/feature/lhc-modes-completion into feature/updatable-dashboard
Created by: andreh12
added missing strings for the code field in class LHCBeamMode (as discussed with @gladky).
Also added a test for class BeamActive whose behaviour will effectively change and do what the code actually intends to do (before it was returning true only for STABLE BEAMS).