improve slider interface

[zakqwy]

experiment with up/down buttons, less resolution, etc.

[NeuroTinkerJoe]

When updating the resolution, it would be worth respanning the virtual membrane potential so that sliding all the way to the left sets the membrane potential at a hyperpolarized (bluish LED) state, which would result in a neuron that is slightly more difficult to fire than normal. Sort of a high pass filter when in this state, which is physiological with some types of neurons. If there are say 4 bits of resolution with the slider, maybe the leftmost possibility is hyperpolarized, and then when sliding to the right, the next step is normal resting membrane potential, maybe the next 4 are elevated but subthreshold potentials, and the final 10 are suprathreshold that lead to increasing firing frequencies.