Add a method to monkey_patch pandas.

Make a way for qgrid to be the default display method for DataFrames, via a new `monkey_patch()` method.

```python
import pandas as pd
import qgrid
qgrid.monkey_patch(pd, remote_js=True)
```

After that, every time a DataFrame is displayed it will now have a `_ipython_display_()` method which renders it as a SlickGrid.