Make offset and amplitude handling of AWG configurable

[terrorfisch]

Currently the AWG-drivers treat the incoming waveforms as if their unit is Voltage and take the respective channels output range into account. However, the offset is ignored. This is because it turned out to be convenient to quickly sweep the offset of a pulse via the offset setting of the awg.

The downside of this is, that the user might expect that the AWG's offset is taken into account when uploading the waveform. I think it is reasonable to add the functionality of ignoring this offset to the AWG interface.

Objections:

• Some AWGs can change such a setting themselves at runtime (HDAWG)