transpose subplots 
Right now its easy to plot columns as rows like this:
df.plot(subplots=True, layout = (15, 1),legend=False) # for a 300x15 dataframe
which gives very nice row plots like this:
![rows](https://cloud.githubusercontent.com/assets/1256202/18203706/e4d66ac2-7118-11e6-9933-22c919ddf1ba.png)

However sometimes it is needed to also plot this as columns instead - so basically swap x and y axes on each subplot. ie. its not enough to just transpose the df before plotting because its the plotting that needs to be transposed and not the data.
Is this possible already somehow? If not, could this possibly be implemented ?
