UP-4223 Fail gracefully in handling profile selection events.

This is a tweak to merged #450 to make handling the `ProfileSelectionEvent` safe.

Failure to persist a profile selection is bad (and is an error, and should be logged so that the portal administrators can address it.)  But failing to persist a profile selection shouldn't fail the entire portal experience for the user.
It's an error.  Something went wrong, the user experience is probably degraded, and a portal administrator probably wants to know about this error and probably needs to do something about it. So I think it should be logged at `ERROR` level.

Of course, even logged at `ERROR` level, an adopter interested in turning off the noise can still suppress it, by differentially configuring logging for `org.jasig.portal.portal.layout.profile.StickyProfileMapperImpl`.  They'll probably be better off fixing whatever is causing the error, though, rather than silencing the canary in the mine. :)