0.7.1 Small fixes, improvements

• Add histogram of leaf sizes with option to filter the leaves with less than min_samples or more than max_samples.
• Added more markersize args
• don't show horizontal bars indicating prediction if no splits requested
• add new color settings:

'scatter_marker_alpha': 0.5,
'tesselation_alpha': 0.3,
'tesselation_alpha_3D' : 0.5,