add viewer to mutationadd

[sibelius]

fix #37

[codecov-io]

Codecov Report

Merging #56 into master will not impact coverage.

@@           Coverage Diff           @@
##           master      #56   +/-   ##
=======================================
  Coverage   82.67%   82.67%           
=======================================
  Files          13       13           
  Lines         202      202           
=======================================
  Hits          167      167           
  Misses         35       35

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[rturk]

This will always include a viewer in the mutation?

[sibelius]

only on add mutation, we can move this as a parameter or as a config later

[lucasbento]

@sibelius: The boilerplate has a ViewerLoader, should we use it or not?

[sibelius]

neh, just return the logged user