Adds maximum step size setting used by transient analysis solver,
and 'use initial conditions (uic)' setting. Enabling uic disables
DC operating point analysis and may introduce singularities. It requires
a careful selection of initial conditions of circuit elements.
Fixes https://gitlab.com/kicad/code/kicad/issues/2515
Also fixes a bug so that voltages, currents and power dissipations are
only probed if the flag is set -- this keeps ngspice from throwing an
error if you probe something twice (for instance, if you have .probe
commands in text and turn off the auto-probing).
Jeff Young
Okan Demir
Wayne Stambaugh