Tool change shortcuts let popovers linger

Some popover destruction code (e.g., the differential partial definition editor) uses the ChartView's presently selected object to write the changes to. However, changing the active tool clears the selected object (since the type of the object should match the type of the tool, and the easiest way to ensure this is to wipe out the selected object).

When clicking in the Toolbar to change the active tool, this is not an issue; the click sends a destruction message to the popover and changes are written before the selected object is blanked out. When using the keyboard shortcuts to change the active tool, the popover is not sent a destruction message, causing a crash when the popover later tries to close and write data to an unfamiliar selected object.

This is easy to fix: just close all active popovers when receiving a keyboard tool change message.