good progress on RoleML-based queries

Got all the easy stuff done today, including a new QTransaction class. What remains is to create an executable pluging for descriptor elements and migrate the existing code the new form. The plugin will be a bit different from Apps, as it needs to work with both Descriptor elements and Descriptor Model elements. Of course, after that we need to implement some basic queries.

Oh yes, one item of interest. Model elements can't resolve pathnames. And for cases where there is no context, then we also need a Rolon to serve as the default context. Well, there's only one Rolon which is always there when you need it--Keywords. So the Keywords rolon is used to resove pathnames and to serve as a default context (i.e. its eval method gets invoked) when there is no other context. A bit of a cludge, but it shouldn't make for too many complications down the road.