Add ability to hide Data and Metrics sections

[laurenwalker]

Since the Data and Metrics tabs are not associated with ProjectSectionModels, they are marked as hidden in the project document by setting the hideData and hideMetrics attributes to true on the ProjectModel. These are serialized as options in the project document XML.

The Data tab will have a "Hide" option instead of "Delete". The ProjEditorSectionView will never be removed from the UI. It be displayed as hidden in some way (this is not in the latest round of mockups).