fix(gestures): fixes scroll issue with hammer config

Fixes scroll issue with hammer config where pinch/rotate gestures are preventing the screen from scrolling.

Closes #6897

src/gestures/ionic-gesture-config.ts

@@ -0,0 +1,25 @@
+import {Injectable} from '@angular/core';
+import {HammerGestureConfig} from '@angular/platform-browser';
+
+/* this class override the default angular gesture config.
+ * The motivation for this is enabling pinch, rotate or
+ * any other multi-touch gestures block scrolling.
+ */
+
+/**
+ * @private
+ */
+@Injectable()
+export class IonicGestureConfig extends HammerGestureConfig {
+  
+  buildHammer(element: HTMLElement) {
+    var mc = new (<any> window).Hammer(element);
+
+    for (let eventName in this.overrides) {
+      mc.get(eventName).set(this.overrides[eventName]);
+    }
+
+    return mc;
+  }
+
+}

src/gestures/test/ionic-gesture-config.spec.ts

@@ -0,0 +1,31 @@
+import { IonicGestureConfig } from '../../../src/gestures/ionic-gesture-config';
+
+export function run() {
+
+  describe('IonicGestureConfig', () => {
+    it('should create a new instance of hammer', () => {
+      // arrange
+      let instance = new IonicGestureConfig();
+      let expectedParam = { name: "expectedParam"};
+      let expectedHammerInstance = { name: "hammer"};
+      
+      let actualParam : any = null;
+      let callCount = 0;
+
+      (<any> window).Hammer = (param: any) => {
+        callCount++;
+        actualParam = param;
+        return expectedHammerInstance;
+      };
+      
+      // act
+      let returnValue = instance.buildHammer( <HTMLElement> <any> expectedParam);
+
+      // assert
+      expect(returnValue.name).toEqual(expectedHammerInstance.name);
+      expect(callCount).toEqual(1);
+      expect(actualParam.name).toEqual(expectedParam.name);
+    });
+  })
+
+}