Added authorization for VariableReference fields

[sungam3r]

See #42 .Thanks @bogdancice

[codecov-commenter]

Codecov Report

Merging #179 (9d6164d) into master (a193954) will increase coverage by 1.09%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##           master     #179      +/-   ##
==========================================
+ Coverage   80.84%   81.93%   +1.09%     
==========================================
  Files           9        9              
  Lines         214      238      +24     
  Branches       32       36       +4     
==========================================
+ Hits          173      195      +22     
- Misses         32       33       +1     
- Partials        9       10       +1     

Impacted Files	Coverage Δ
...aphQL.Authorization/AuthorizationValidationRule.cs	94.93% <91.66%> (-1.43%)	⬇️

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[sungam3r]

@Shane32 I want to merge this ASAP and go on. I'll make suggestions from code review later if you have any.

[Shane32]

Looks fine.

[sungam3r]

Almost - #182 :)