BUG: Better axis label handling for partial layout

[sinhrks]

Closes #5897.

Handle ticklabels and labels based on below rules. Currently labels are always displayed even if ticklabels are hidden and causes confusion.

• If sharex is True, display only most bottom xticklabels on each columns. (Because ENH/BUG: boxplot now supports layout #7035 hides the bottom-right axes). Hide xlabel as the same manner as xticklabels
• If sharey is True, display most left yticklabels (no change). Hide ylabel as the same manner as yticklabels (changed)

import pandas as pd
from numpy.random import randn
import matplotlib.pyplot as plt

d = pd.DataFrame({'one':randn(5), 'two':randn(5), 'three':randn(5), 'label':['label'] * 5},
        columns = ['one','two','three', 'label'])
bp= d.boxplot(by='label', rot=45)

[jreback]

@cpcloud

[jreback]

@cpcloud ?

[jreback]

@cpcloud ? @sinhrks can you rebase

[jreback]

thanks!