Feature request: groupby.plot() and groupby.hist() add groupname as figure title
Hello!
I'm plotting histogramms and line plots from a groupby - object. It works fine and for each group a figure is generated. But i think a nice feature would be to automatically add the groupname (label) as figure title to each figure. Below you can see a line and a histplot from one group

![groupby_plot](https://cloud.githubusercontent.com/assets/16588610/13347557/e6c79fde-dc6e-11e5-8f12-e467b8bb3913.png)
![groupby_hist](https://cloud.githubusercontent.com/assets/16588610/13347556/e6c51e94-dc6e-11e5-84b4-d31323e95af6.png)

My code:

```
import os
import sys
import datetime
import matplotlib.pyplot as plt
import pandas as pd
import matplotlib.dates as mdates
import numpy as np


%matplotlib notebook


dates = pd.date_range('2013-07-14 11:00:00', '2013-07-16 11:00:00', freq = 's')
cats = np.random.choice(['m', 'f', 'c'], len(dates))
data =np.random.randn(len(dates),1)
data2 =np.random.randn(len(dates),1)

df = pd.DataFrame(data, dates)
df.columns = ['data']
df['cats']= cats
df['data2'] = data2

plt.figure()
ax1 = df.groupby('cats').hist(bins=20, normed=True) #Figure1
#ax1 = df.groupby('cats').plot(subplots=True, layout=(3,1)) #Figure1
plt.figure()
ax1 = df.groupby('cats').plot() #Figure1

```

Pandas:

```
pd.__version__
'0.18.0rc1'

```
