#17 enable/disable each Quick View depending on working set

[Rob Lintern]

I wonder if it would be simpler to have the working sets
changed at project load time only and then have the
available quick views only be enabled for things in the
working set.. When the user mouses over a disabled
quick view the user could be asked if the project can be
reloaded with the working set expanded to include those
arc/node types... However I wouldn't remove other
things from the working sets as the user will be
surprised (sometimes that seems to happen).