wywsiwygb export of supporting data for figures

Jalview's figure export is based on an alignment view's visual settings, so when supporting data is exported alongside a figure (e.g as bioJSON) then all necessary data should be preserved to allow the view to be recreated with a minimum of dataloss.

As a first step - if hidden columns are included, the export should mark columns as hidden rather than stripping them out, similarly for features, etc. This amounts to automatically setting the 'export settings' checkboxes appropriately, and warning the user that they may lose data if those settings are changed.

There are some corner cases that also need looking at - sometimes one wants to export exactly the data that is required to reproduce the figure, and other times, one may want to export all data associated with the figure. The latter is accomplished by the Jalview project file - so it might make sense to allow a per-view project to be exported along-side a figure in order to allow the figure to be reproduced afterwards.

Oh - wywsiwygb is:
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