Improve data used in DecisionTreesExample

Data currently used in DecisionTreesExample looks not quite optimal:

1. It is large, as evidenced in the warning in javadocs: "It is recommended to start at least one node prior to launching this example if you intend to run it with default memory settings."
2. It makes example run for quite a long time.
3. It doesn't have license (likely meaning "all rights reserved" by default) which makes it troublesome to include in project sources so that current approach is to prompt user to download it, additionally complicated by making example skip when run unattended from IgniteExamplesMLTestSuite.

Suggest to find or construct a smaller data for this example which would still make sense to demonstrate how algorithm works and in the same time would be 1) easier on memory usage, 2) quicker to run and 3) would allow carrying it within project instead of prompting user to download it.