Create parent formatter that allows selecting how many levels of lineage to traverse

Ok, I created a field formatter that is the first step towards this issue. Right now it just displays the label of the root parent of a tree.

Remaining tasks:

• Fix the "link to referenced entity" feature to link to the root entity instead of the direct parent.
• Add configuration to specify which level of parent (grandparent, great grandparent, etc.) to display.
• Add tests.

sim_1 → closed merge request !14

Oops, I created a branch targeting the 8.x-2.x branch at first. Deleted that MR and remade one for the 3.x branch.