Expanded code delta API

[fo-code]

I expanded the API for calculating the code delta with another method which calculates the delta between two Jenkins builds.

[codecov]

Codecov Report

Merging #406 (1222adc) into master (60fd4a7) will increase coverage by 0.24%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #406      +/-   ##
============================================
+ Coverage     68.44%   68.69%   +0.24%     
- Complexity      365      370       +5     
============================================
  Files            48       48              
  Lines          1160     1169       +9     
  Branches        100      100              
============================================
+ Hits            794      803       +9     
  Misses          325      325              
  Partials         41       41              

Impacted Files	Coverage Δ
...nkins/plugins/forensics/delta/DeltaCalculator.java	100.00% <100.00%> (ø)
.../jenkins/plugins/forensics/delta/model/Change.java	100.00% <0.00%> (ø)

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