Checks needed when updating a widget to be a singleton

[denialg]

When editing a widget, it is possible to cause an error in OWF if you edit it to be a singleton while there are multiple instances of a widget open in a dashboard. There should probably be some logic to verify that the widget in question is not already present multiple times in a dashboard

To recreate (steps courtesy of Neil Castine):

1. Create a dashboard with a vertical divider.
2. Set a portal pane on the left and a desktop pane on the right.
3. Launch two instances of the same normal widget and place one in each pane.
4. Edit the properties of said widget changing it to be both singleton and background.
5. Refresh the browser and error occurs.

[colemanserious]

From a usage perspective... what should then occur if it is in use?

Options that come to mind:

• allow it to be set as singleton, but provide the user with a dashboard in this state some better message and way to remove the extra instance / contact an administrator
• give the administrator a way to find those dashboard instances and work with users.. (presumably there's a reason to make it a singleton)
• not allow the administrator to set that widget instance up as singleton, but instead create a new widget definition, and potentially mark the existing one as not usable in new dashboards...

Also, presumably it being in background, as well as singleton, just makes it harder to discover the offending widget?