Added dependency on commons-math3

[smoe]

Without that dependency, many build errors pop up:

/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/MathUtil.java:32: error: package org.apache.commons.math3.special does not exist
import org.apache.commons.math3.special.Gamma;
                                       ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/MathUtil.java:33: error: package org.apache.commons.math3.util does not exist
import org.apache.commons.math3.util.FastMath;
                                    ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:3: error: package org.apache.commons.math3.special does not exist
import org.apache.commons.math3.special.Beta;
                                       ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:4: error: package org.apache.commons.math3.special does not exist
import org.apache.commons.math3.special.Erf;
                                       ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:5: error: package org.apache.commons.math3.special does not exist
import org.apache.commons.math3.special.Gamma;
                                       ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:6: error: package org.apache.commons.math3.util does not exist
import org.apache.commons.math3.util.FastMath;
                                    ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:7: error: package org.apache.commons.math3.util does not exist
import org.apache.commons.math3.util.MathUtils;
                                    ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:9: error: package org.apache.commons.math3.special does not exist
import static org.apache.commons.math3.special.Beta.regularizedBeta;
                                              ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:9: error: static import only from classes and interfaces
import static org.apache.commons.math3.special.Beta.regularizedBeta;
^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:10: error: package org.apache.commons.math3.util does not exist
import static org.apache.commons.math3.util.CombinatoricsUtils.binomialCoefficientLog;
                                           ^
/home/moeller/git/med-team/vdjtools/vdjtools/src/main/java/com/antigenomics/vdjtools/misc/StatUtil.java:10: error: static import only from classes and interfaces
import static org.apache.commons.math3.util.CombinatoricsUtils.binomialCoefficientLog;