Add warmmiete calculation logic and related metadata; implement custom view for warmmiete field

client/custom/src/views/c-vmh-mietverhaeltnis/fields/warmmiete.js

@@ -0,0 +1,38 @@
+define('custom:views/c-vmh-mietverhaeltnis/fields/warmmiete', ['views/fields/currency'], function (Dep) {
+
+    return Dep.extend({
+
+        setup: function () {
+            Dep.prototype.setup.call(this);
+
+            this.calculating = false;
+
+            // Listen to changes on dependent fields
+            this.listenTo(this.model, 'change:kaltmiete', this.calculate.bind(this));
+            this.listenTo(this.model, 'change:bKVorauszahlung', this.calculate.bind(this));
+            this.listenTo(this.model, 'change:bKPauschale', this.calculate.bind(this));
+        },
+
+        afterRender: function () {
+            Dep.prototype.afterRender.call(this);
+            // Don't calculate on initial render - only on changes
+        },
+
+        calculate: function () {
+            if (this.calculating) return;
+            this.calculating = true;
+
+            var kaltmiete = parseFloat(this.model.get('kaltmiete')) || 0;
+            var bKVorauszahlung = parseFloat(this.model.get('bKVorauszahlung')) || 0;
+            var bKPauschale = parseFloat(this.model.get('bKPauschale')) || 0;
+
+            var warmmiete = kaltmiete + bKVorauszahlung + bKPauschale;
+
+            // Set value - this will trigger the parent view to update
+            this.model.set('warmmiete', warmmiete);
+
+            this.calculating = false;
+        }
+
+    });
+});