Prework

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Description

The shiny app launched by tar_watch updates every few seconds (5 by default). While the update is in process, the network is replaced by a "loading image" (from package shinycssloaders). As this update takes about 1 second, I think it would be more useful to leave the native shiny behavior during the update - continue to show the image that is about to be replaced. It's visually jarring to have the image continually disappearing and reappearing.