Add employeesIds to the base job class

...and make it function as its sisters are (was a property).

src/004-base/facility.js

@@ -156,6 +156,14 @@ App.Entity.Facilities.Job = class {
 			(acc, cur, idx) => { if (cur.assignment === this.desc.assignment) { acc.push(idx); } return acc; }, []);
 	}
 
+	/**
+	 * IDs for all slaves that are employed at this job
+	 * @returns {number[]}
+	 */
+	employeesIds() {
+		return this.employees().map(s => s.ID);
+	}
+
 	/**
 	 * Tests if slave is broken enough
 	 * @protected
@@ -332,7 +340,7 @@ App.Entity.Facilities.Facility = class {
 	 * @returns {number} */
 	get hostedSlaves() {
 		const job = this.job();
-		return job ? job.employeesIds.length : 0;
+		return job ? job.employeesIds().length : 0;
 	}
 
 	get hasFreeSpace() {
@@ -560,7 +568,7 @@ App.Entity.Facilities.FacilitySingleJob = class extends App.Entity.Facilities.Jo
 		return ids.map(id => si[id]);
 	}
 
-	get employeesIds() {
+	employeesIds() {
 		return State.variables[this._employeeIDsVariableName]; // updated by assignJob()/removeJob();
 	}