updateIndex(allEdgeTypes) {

    const allSubscribers = [];

    // instantiate and register all active subscriber modules
    const subscriberClass = this.subscriberClasses;
    for (let moduleName in subscriberClass) {

      const subscriber = new (subscriberClass[moduleName])(allEdgeTypes);
      subscriber.setTracker(this.tracker);

      // ignore all subscribers that have their ignore flag set to false
      if (subscriber.ignore === true) {
        continue;
      }

      allSubscribers.push(subscriber);
    }

    // sort subscribers by priority
    allSubscribers.sort((s1, s2) => s2.priority - s1.priority);

    this.allSubscribers = allSubscribers;

  }
Indexes all subscribers. Moreover, subscribers get linked to the edge
types that currently exist in the wiki.

This method should be called everytime after an edge type is added or
removed in the system.

@param {EdgeType[]} allEdgeTypes