Update get_scatter_matrix for sparse dataframes
Update get_scatter_matrix for sparse dataframes

For a dataframe like:

	A	B	C
0	1.0	7.0	NaN
1	2.0	8.0	NaN
2	3.0	9.0	NaN
3	4.0	NaN	13.0
4	5.0	NaN	14.0
5	6.0	NaN	15.0
6	NaN	10.0	16.0
7	NaN	11.0	17.0
8	NaN	12.0	18.0

the 'Interactions' tab would not display any data (as all rows contain NaN's) while any pair of columns would contain valid data to plot.
This change allows columns A, B, and C to be pairwise plotted against each other by only removing rows with NaN's between the pairwise columns.
JosPolfliet/pandas-profiling,JosPolfliet/pandas-profiling