Implement linkage disequilibrium measurements

[magicDGS]

• Linkage disequilibrium determinant (D) and normalized version (D')
• Pearson correlation (r^2), including signed correlation (rw)
• Normalized r^2 and maximum r^2 reached by concrete frequencies
• Test for r^2 significance with Chi-Square distribution

Closes #7

[codecov[bot]]

Codecov Report

Merging #25 into master will increase coverage by 0.579%. The diff coverage is 97.778%.

@@               Coverage Diff               @@
##              master       #25       +/-   ##
===============================================
+ Coverage     95.604%   96.183%   +0.579%     
- Complexity        41        64       +23     
===============================================
  Files              4         5        +1     
  Lines             91       131       +40     
  Branches           5        10        +5     
===============================================
+ Hits              87       126       +39     
- Misses             4         5        +1

Impacted Files	Coverage Δ	Complexity Δ
...a/org/magicdgs/popgenlib/utils/FrequencyUtils.java	97.826% <100%> (+0.458%)	14 <7> (+3)	:arrow_up:
...icdgs/popgenlib/linkage/LinkageDisequilibrium.java	96.875% <96.875%> (ø)	20 <20> (?)