Support CMV data structure in the pivot model

[JakobVogelsang]

As a user of FledgePower I need to be able to send measure value throught he IEC 61850 south plugin to the 104 north plugin. Measured value are often coded as MMXU.A.phsA with is a cdc CMV holding both the magnitude as well as the - optionally - the angle of a phasor. This is at the moment missing in the pivot model as far as I can see.