Modified the tests that compare previous gpu & feature tables as follows:

Previously, the viewer stored the GPU class, and if that changed then preferences were reset.   This submission changes the test to be based on the GPU id string rather than the GPU class, so that reclassification will not cause preferences to be reset.  If the actual GPU has changed, such as a new computer, a new video card, or even a new driver, it is ok to reset the preferences.  I have made a new dialog that shows the previous and new GPU identifiers, so the user can see exactly why the preferences have been changed.   This should be infrequent and unsurprising.  

The other, and most frequent, cause for graphics preferences being reset is that something in the featuretable has changed, and the version number of the table has been incremented.  Since we want to retain the ability to force values back to the recommended settings, this has been retained, but the rule has now been made explicit that the version number should be incremented ONLY if resetting all preferences is the intended effect, and not for just any change to the table.  The notification dialog for this case has also been made more explicit.

Manually simulated changes of both conditions, and the new dialogs were displayed correctly and preferences were reset.  Also ran without changing anything, and preferences were preserved.