HHChannel/HHGate: Give warning if min, max, divs are not set

[subhacom]

When directly setting the gate tables, users often forget/unaware of setting min, max, and divs attributes of HHGate objects.
A warning at reinit will help avoid hard to figure out bugs in user code.

[analkumar2]

Same for the the useConcentration field. It is by default True and if one is using the Z gate without setting useConcentration, it gives unexpected results without throwing any errors.