BUG: allow series to use gcf-style figures
cc @fonnesbeck

here's the original issue: https://github.com/pydata/pandas/commit/51cc9d9d21554701f70ef24392bd78a3da189335#commitcomment-3494266

@fonnesbeck can u try this out? @jreback any thoughts?
 @jreback couple of things here: possible issue is the new-ish API change that if `figure` and `by` are given an error will be raised saying that you cannot pass `figure` and `by` since the `figure` will be discarded with grouped hist plots; i feel like this is something @wesm might give a big :-1: to...personally i would prefer to get an error telling me my passed figure won't be used. OTOH i could certainly make `_subplots` take a figure argument.
 @jreback can we get this in to 0.12?
 is what `Series.plot` does (take from the current figure)?
 yep
 looks reasonable
 actually what i said was slightly wrong: nothing is done with the figure unless the current axis has ticks on the right yaxis.
 this looks fine to me
 will merge after failing test fix
