Graph UI, controls and feature improvements as follows:

 * Make mouse busy on any blocking operation
 * Ensure buttons are disabled when mouse actions are happening
 * Better button layout, easier to remember and use
 * Implement "remove all vertices except from latest query" button
 * Implement "add vicinities of latest query" button
 * Implement "converged" state, offer reset and terminate
 * GraphAggregator also keeps track of highest/lowest state and sends it along