A multi-channel driving Profile for any application where experimentally
a digital to analog conversion would be employed. It is based primarily on
the requirements of voltage and current clamp patch studies where the same
command may be repeated several times (nstep) with increments in particular
sections and a pause (ms) between repeats. The nrepeat field is for repeating
the whole series of steps which is only useful in a model if
some pseudo-random process is being explored such as stochastic channel
activity or noise.
user interface: SteppedProfileEditor
|     field |     type   |     contents / default value |     |
| units | choice | variable: units type: choice | |
| nstep | integer | 6 | variable: nstep type: integer |
| pause | double | 100.0 | variable: pause type: double |