[Future iteration] => Allow seed-wide variables

Problem

There could reside a lot of duplication in seeding.

Given this seed file ...

---
group_labels:
  - title: Label 1
    color: "#FF0000"
  - title: Label 2
    color: "#FF0000"
  - title: Label 3
    color: "#FF0000"
  - title: Label 4
    color: "#FF0000"
  - title: Label 5
    color: "#FF0000"
  - title: Label 7
    color: "#FF0000"
  - title: Label 7
    color: "#FF0000"
  - title: Label 8
    color: "#FF0000"
  - title: Label 9
    color: "#FF0000"
  - title: Label 10
    color: "#FF0000"

Each label has duplicated content (namely, the color). If this color ever changes, each line will need to be changed.

Proposal

To encourage de-duplication, provide a way to specify variables that can be referenced anywhere in a seed file.

---
_label_color: "#FF0000"

group_labels:
  - name: Label 1
    color: <%= _label_color %>
  - name: Label 2
    color: <%= _label_color %>
  - name: Label 3
    color: <%= _label_color %>
  - name: Label 4
    color: <%= _label_color %>
  - name: Label 5
    color: <%= _label_color %>
  - name: Label 6
    color: <%= _label_color %>
  - name: Label 7
    color: <%= _label_color %>
  - name: Label 8
    color: <%= _label_color %>
  - name: Label 9
    color: <%= _label_color %>
  - name: Label 10
    color: <%= _label_color %>