ResultEntitySource interface + CsvResultEntitySource impl

[johanneshiry]

Resolves #388

[johanneshiry]

!test

[codecov]

Codecov Report

Merging #389 (2b8ca4e) into dev (c58ef33) will increase coverage by 0.11%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                dev     #389      +/-   ##
============================================
+ Coverage     78.56%   78.68%   +0.11%     
- Complexity     2046     2073      +27     
============================================
  Files           254      255       +1     
  Lines          8124     8160      +36     
  Branches        767      767              
============================================
+ Hits           6383     6421      +38     
+ Misses         1353     1352       -1     
+ Partials        388      387       -1     

Impacted Files	Coverage Δ
...datamodel/io/source/csv/CsvResultEntitySource.java	76.47% <0.00%> (ø)
...factory/result/SystemParticipantResultFactory.java	93.93% <0.00%> (+1.51%)	⬆️
...edu/ie3/datamodel/io/source/csv/CsvDataSource.java	94.31% <0.00%> (+4.08%)	⬆️
.../models/result/system/SystemParticipantResult.java	45.83% <0.00%> (+4.16%)	⬆️
.../edu/ie3/datamodel/models/result/ResultEntity.java	50.00% <0.00%> (+4.54%)	⬆️

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[baszach]

@johanneshiry do you think we can approve and merge this PR? Please, take a look at the test I wrote (CsvResultEntitySourceTest) and tell me if it needs changing/additions.