Controlling whether data sets show in legend.

First step for [#37445619]. This should fix [#41907551] as well.
Making to_hash show the right in_legend value.

This is for [#37445619] but also finishes [#41907551]. Note that the spec is getting rewritten a bit, partly because of the way the graph-pane to data set relationship works but also partly because of this: http://blog.davidchelimsky.net/2012/05/13/spec-smell-explicit-use-of-subject/
Finishing legend-sensitive data-set serialization

Extends changes made in PredefinedGraphPanes for [#37445619] and [#] to PredictionGraphPanes and SensorGraphPanes. Note that the included_datasets hashing helper method has been factored back out of sg_graph_pane and into the models themselves due to the relationship naming differences.
Testing adding in_legend to data_set join model
Trying changed view hints for join
Whitespace cleanup
Cards for SensorPane/DataSet relationship models

[#37445619]
Merge branch 'master' into graph-pane-data-legends

Getting the "children" viewhints for in_legend work
Hiding obsolete association form
Viewhints to show join instead of datasets

Extending this change to PredictionGraphPane and SensorGraphPane.
Form for adding DataSets to GraphPanes with legend

This handles [#37445619]. The form turned out to be easier than I'd feared in the end. This commit does PredefinedGraphPanes; the next will extend the solution to PredictionGraphPanes and SensorGraphPanes.
Oops (wrong parent set in PredictionGraph)
Legend configuration for prediction and sensor graphs

Should wrap up [#37445619] except for some interface oddities
Suppresses the "new DataSetPredictionGraphPane" link

[#37445619]
Cleaning up unnecessary tags in show pages
Revert "Cleaning up unnecessary tags in show pages"

Maybe this wasn't so unnecessary after all.

This reverts commit 3724a6bdcb6ee7103febf92fc031d671c0df1c01.
Reverts removal of selecting included graphs
Splits selection of data sets in cucumber based on UI
Selecting datasets now requires JS
inLegend now defaults to false

This changed for [#41907551]