Minor inconsistency between MPC and MGCP event names

[andig]

Consider this difference (current vs currents):

mpc.DataUpdateCurrentsPerPhase
mgcp.DataUpdateCurrentPerPhase

vs

mpc.DataUpdateVoltagePerPhase
mgcp.DataUpdateVoltagePerPhase

Not sure if this is from the spec or internal. If you want to let me know which variant you prefer (DataUpdateCurrentPerPhase in line with voltages) I'd be happy to open PR and also check remaining use cases.

Note that the interface is also mpc.CurrentPerPhase. The event name seems to be the odd outlier.