Add Export flag to charts

[jwildfire]

Summary

Adds support for a new Export flag in chart config objects. If the flag is true, the chart shows up on the reports list, if false it doesn't. If no export flag is set, it defaults to true. The flag is currently overridden when type="module" since they cannot be exported.

With the updates here and in safetyCharts SafetyGraphics/safetyCharts#52 all charts should have basic functionality in the exported html document.

Test notes

Make sure all exported charts work as expected using the following branches:

devtools::install_github("safetyGraphics/safetyCharts", ref="fix-49")
library(safetyCharts)
devtools::install_github("safetyGraphics/safetyGraphics", ref="reports-updates")
library(safetyGraphics)
safetyGraphics::safetyGraphicsApp()

[elimillera]

Still having trouble with the Hepatic Safety Explorer. I'm thinking it must be a package or a dependency I don't have.

Otherwise everything looks good.