Level tree functionality can be improved

[rensink]

The level tree, showing (and allowing to select and include/exclude) quantifier levels in a nested rule, can be improved in several ways.

• When selecting/excluding a named level, the corresponding quantified edges are not taken into account
• Dually, a node with such a quantified edge (as above) should remain included if the named level is included
• Excluding a given level could passively exclude all sublevels
• In the rule system below, excluding E.1.0 of rule fired incorrectly excludes the RuleOcc node

build-occurrence-graph-stepwise-rs.gps.zip