Fix/1776 printing blinded labels

[leandroradusky]

Closes #1776.

To correctly print the blinded attributes, both in the normal and the bulk print, the SamplePresenter object is passed to the PDF generator (instead of Sample as it was before, which wasn't blinding.

Before, incorrectly, blinded attributes were printed, now we can observe they don't:

[ysbaddaden]

Neat!

I'm just not fond of form in the naming since they're not a SampleForm it could be confusing. Maybe we can just avoid naming a variable? For example:

locals: { sample: SamplePresenter.new(@sample, request.format) }

locals: { samples: samples.preload(:sample_identifiers).map { |s| SamplePresenter.new(s, request.format) } }