A little documentation for linked animations
Makes GraphLabel parent polymorphic to enforce single-parent

Following up on this idea: http://stackoverflow.com/a/18726662/306084 which came from the attempt to make a GraphLabel belong to a LabelSet or a PredefinedGraphPane, but not both. Previously we simply didn't offer Labels which already belonged to a LabelSet as options to link to PredefinedGraphPanes, and we'll keep that in place, but now if you do manage to link a GraphLabel to a PredefinedGraphPane, it will be removed from its LabelSet when that happens.
Fixing 'included graphs' label for PredefinedGraphPanes

[#56372392] Makes it "included prediction graphs". Also, a slew of help text additions, which turn out to live in the localization file.

https://www.pivotaltracker.com/story/show/56372392
Fix display of DataSets in PredefinedGraphPane

This should finish [#56372392]

https://www.pivotaltracker.com/story/show/56372392
Clean up
WIP: showing too many labels in menus