Label for CheckGroup

CheckGroups now have a label property that is passed in the config and drawn as a header for the bric.
542: Data Report: Item Detail - Instructor View

Jira: RC-542
fix comment typo
359: add expected properties in discussions response from LocalAnswerMan

Jira: BRIX-359
359: enhance the LocalDiscussionMan

Jira: BRIX-359
359: make localanswerman work with localdiscussionman when submitting discussions assessmenttypes

Jira: BRIX-359
359: add discussionMan parameter to SubmitManager constructor

I also created a SubmitManager.Config typedef, but there are 84 current uses of the SubmitManager in demo, src and tests that have to be updated in order to change the constructor signature to use a config object.

That's a project for a different commit.

Jira: BRIX-359
changed ITop & IBottom interfaces to support converting a display point to a data point

- changed ITop.setDataPtToDisplayPtFn to setPtConversionFns to also set displayPtToDataPtFn

- removed getScaleX and getScaleY public methods from LineGraph and BarChart

- implemented displayPtToDataPt methods, which convert physical coordinates to logical coordinates for linear scales, and throw errors for ordinal scales

- update the following Brix:
  - IBottom
    - LineGraph
    - BarChart
    - Sketch
    - CaptionedImage
  - ITop
    - LabelGroup
    - Image
    - Sketch

Note that the Axes have not been enhanced to provide the invertScale function, which is particularly relevant to ordinal axes since the d3 ordinal scale doesn't provide one we could just return directly.

This affects BarChart whose displayPtToDataPtFn will throw an error until this is implemented.