Flattened Person-Worktype facets for Sankey Visualizations

[jrhoads]

• Formatting
• Facet processing for multi-level facet with contributors and work-typs
• Facet processing to flatten multi-level facets
• Add multi-level and flat facets for person-worktypes
• Appease Rubocop
• Add specs for multi-level and flattened facets
• Appease Rubocop

Purpose

Provide a flattened facet for person-worktypes
To be used in Sankey diagrams for DMPs
Can be used for any collection of works.

closes: datacite/datacite#1913

Types of changes

• Bug fix (non-breaking change which fixes an issue)

• New feature (non-breaking change which adds functionality)

• Breaking change (fix or feature that would cause existing functionality to change)

Reviewer, please remember our guidelines:

• Be humble in the language and feedback you give, ask don't tell.
• Consider using positive language as opposed to neutral when offering feedback. This is to avoid the negative bias that can occur with neutral language appearing negative.
• Offer suggestions on how to improve code e.g. simplification or expanding clarity.
• Ensure you give reasons for the changes you are proposing.

[digitaldogsbody]

Looks good to me :)