Implement a dummy/simulation AWG

[shumpohl]

Implement an AWG class that tranforms programs into a simple time voltage relation and feeds it into a callable (e.g. a simulation).

Required features:

• Variable sample rate
• Maximum chunk length

Optional features:

• optimized Δt format of output to reduce workload for long times with same voltage

This is a first step towards #2 and #10

[shumpohl]

First draft in issues/421_virtual_awg

Variable sample rate and maximum chunk length are not implemented to cut down development time. They seem to be premature optimization and can still be added when a performance problem arises.