ENH: Add functions to summarize a single template

Previously we could only summarize two templates i. e. requiring that
the user passed a sample and a prep template. This code has been
reworked to only require a template-like object.

Fixes #415
ENH/BUG: Correctly display unique/repeated values

Fixes #541
STY: Add suggestions from @antgonza
STY: Move study_id to the top of the handler
STY: 😱📲
STY: flake-it-up 📲
ENH: Only instantiate one study object

We were instantiating several of them and this will reduce some extra
overhead.
Merge pull request #543 from ElDeveloper/issue-415

Show only a sample or a prep metadata summary