Refactor additional properties utility methods

[iainmcgin]

The previous changes made were introducing too much duplicate code, increasing the likelihood of inconsistent future modifications and bugs. This change refactors the implementations into the utils class, and uses parameterized unit tests to check that all implementations are consistent, without affecting the convenience of the API.

This finishes the implementation of #99.

[codecov-io]

Codecov Report

Merging #122 into master will increase coverage by 0.46%. The diff coverage is 97.53%.

@@             Coverage Diff              @@
##             master     #122      +/-   ##
============================================
+ Coverage     70.65%   71.11%   +0.46%     
- Complexity      469      480      +11     
============================================
  Files            65       65              
  Lines          2675     2690      +15     
  Branches        255      246       -9     
============================================
+ Hits           1890     1913      +23     
+ Misses          705      701       -4     
+ Partials         80       76       -4

Impacted Files	Coverage Δ	Complexity Δ
...a/org/openyolo/protocol/CredentialSaveRequest.java	86.88% <100%> (+1.43%)	11 <3> (+2)	:arrow_up:
...rotocol/java/org/openyolo/protocol/Credential.java	92.3% <100%> (+1.39%)	20 <3> (-1)	:arrow_down:
...org/openyolo/protocol/CredentialDeleteRequest.java	93.47% <100%> (+3.09%)	9 <3> (-1)	:arrow_down:
...rg/openyolo/protocol/CredentialRetrieveResult.java	91.66% <100%> (+1.92%)	12 <3> (-1)	:arrow_down:
...g/openyolo/protocol/CredentialRetrieveRequest.java	78.89% <100%> (+0.63%)	14 <3> (-1)	:arrow_down:
protocol/java/org/openyolo/protocol/Hint.java	92.37% <100%> (+0.4%)	21 <3> (+2)	:arrow_up:
...java/org/openyolo/protocol/HintRetrieveResult.java	90% <100%> (+0.93%)	11 <3> (+2)	:arrow_up:
...ava/org/openyolo/protocol/HintRetrieveRequest.java	92.38% <100%> (+0.46%)	14 <3> (+2)	:arrow_up:
.../org/openyolo/protocol/CredentialDeleteResult.java	98.43% <100%> (+2.72%)	11 <3> (-1)	:arrow_down:
...va/org/openyolo/protocol/CredentialSaveResult.java	91.93% <100%> (+0.86%)	10 <3> (+2)	:arrow_up:
... and 1 more

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[iainmcgin]

Proposed changes made.

[iainmcgin]

To unblock David in cutting a 0.2.1 release, I'll go ahead and merge this. @StanKocken we're past the two day review period, if you have any comments please do still submit them and I'll fix in follow-up.