HELP -- Random forest

Not only is mSE (similar to variance) very high for the tree, the variable importance only works for whatever variable is stored in index `0`.  Any ideas why?

While individual random trees did a great job on the test data, the random forest (which after all is just averaging 100 random trees) is preforming very badly.

Data generation:
```java
int n = 200;
DataPoint[] data = new DataPoint[n];
String[] inputKeys = {"A", "B"};
String[] outputKeys = {"Z"};
double[] minimums = {0, 0};
double[] maximums = {100, 100};
for (int i = 0; i < n; i++) {
	double randA = Math.round(Math.random() * 100);
	double randB = Math.round(Math.random() * 100);
	double[] input = {randA, randB};
	double[] output = {(randA > randB) ? 20 : -5};
	data[i] = new DataPoint(inputKeys, input, outputKeys, output);
}
```

(Basically just creates two random numbers and if 1st one is bigger than second one outputs `20`, otherwise outputs `-5`).

@MaxNotarangelo 
@MaxOrth 

Issue #21