Add sampling option to heatmap widget.
Merge pull request #142 from astaric/heatmap-on-sample

Add sampling option to heatmap widget.
Added color scale options.
Time-based sampling on heatmap.
Insure at least some coloring for non zero cells.
Merge pull request #144 from astaric/time-based-sampling

Time-based sampling on heatmap.
Use the actual maximum contingency value for scaling factor.

Before the maximum value in the root was used.
Change sampling options.
Undo change to n_bins.
Merge pull request #145 from ales-erjavec/heatmap

Heatmap color scale
Revert to no outlines.
Initial code for tree viewer.
Initial code for tree graph.
Classification tree visualization: number of nodes, rules.
Added counts of zero for classes not present in internal nodes.
Basic functionality of Classification tree visualization.
Flatten array to resolve bug.
Flatten array to resolve bug, get the number of classes via tree_ object in owclassificationtreegraph.py.
Visualization for classification tree.
Merge branch 'class_tree_viz' of https://github.com/mstrazar/orange3 into class_tree_viz

Conflicts:
	Orange/widgets/classify/owclassificationtreegraph.py