[#37445533] Initial models: Graph Panes can include multiple datasets.

https://www.pivotaltracker.com/story/show/37445533
WIP: stashy.
Use a tagged generator git release until multiple_data_sets is merged.

The generator code and authoring systen need to be kept in sync. Once we
merge in the authoring tools from multiple_data_sets branch,
we can untag our generator dependency.
Update Smartgraphs runtime with Sensor Applet fixes [#37044931]

Richard:
https://github.com/concord-consortium/Smartgraphs/commit/f2e8b0c09672
Update Smartgraphs runtime with Sensor Applet fixes [#37044931]

Richard:
https://github.com/concord-consortium/Smartgraphs/commit/f2e8b0c09672
Merge branch 'master' into multiple_data_sets
simple helper script to build the SmartGraphs runtime.
Merge branch 'master' into multiple_data_sets
Add guard to run spec tests.
Merge branch 'master' into multiple_data_sets
Use rb-fsevent to drive guard.
Merge branch 'multiple_data_sets'
Update spec tests for multiple DataSet GraphPanes.
Run rspec when spec files change.
Move some GraphPane hash attributes into DataSet.
rm from PredefGraphPane methods moved to DataSet

activity_filter_spec fails now because ... ?
Use create!() to trigger immediate failure on object creation for test.

Validation errors were preventing our test participants from being created.
This caused test failures with obfuscated root causes.
Failing faster helps us identify the validation errors.
Use DataBaseCleaner in rspec as well cucumber tests.

We were having trouble with data persisting between tests.
Digging deeper, it was probably related to DataBaseCleaner (in gem file)
see: https://github.com/bmabey/database_cleaner
[#37445533] # fields being moved from PredefinedGraphPane → DataSet

indicate with comments which fields are being moved to DataSet.

https://www.pivotaltracker.com/story/show/37445533
[#37445533] specs for PredefinedGraphPane#included_datasets

https://www.pivotaltracker.com/story/show/37445533