Predefined Graph Pane can have a label

[#46492277] This is just the data model change.
Looks like has_many not has_one
UI for adding Labels to PDGPs

[#46492277]
Output PDGP labels to hash [#46492277]
Spec test for label serialization in PDGP
Refactoring PredefinedGraphPane spec test
Merge branch 'pdgp-single-label' into pick-a-label-set

Conflicts:
	app/models/predefined_graph_pane.rb
	app/models/sg_graph_pane.rb
	app/views/taglibs/front_site.dryml
	db/schema.rb
	spec/models/predefined_graph_pane_spec.rb
Not going down the label_sets in pick-a-point road
This spec was ridiculous
Adding names to labels

This is so they can be referenced as individual objects, instead of only within LabelSets. [#46033607]
PickAPointSequences may have GraphLabels.

[#46033607]
Force a label if answer_with_label is true

[#46033607]
Fix a bad spec merge
WIP: Adding single labels to PredefinedGraphPanes.

This isn't working yet. We're getting a Permission Denied error when loading the PredefinedGraphPane form: "Not allowed to edit graph_label."
Get the fields right for labels in PredefinedGraphPanes
Serialize label names, not label hashes
Spec shouldn't expect whole label, just a name
Merge branch 'label-a-point'
No form fields for adding labels to for-users LabelSet

[#47821301]
Removes superfluous spec