feat(sideMenu): make android back button close side menu

Closes #1264

test/unit/angular/controller/sideMenuController.unit.js

@@ -0,0 +1,37 @@
+describe('$ionicSideMenus controller', function() {
+  beforeEach(module('ionic'));
+
+  function setup(locals, props) {
+    var ctrl;
+    inject(function($controller, $rootScope) {
+      var scope = $rootScope.$new();
+      ctrl = $controller('$ionicSideMenus', angular.extend({
+        $scope: scope,
+        $attrs: {}
+      }, locals || {}));
+      angular.extend(ctrl, props || {});
+    });
+    return ctrl;
+  }
+
+  it('should register with backButton on open and dereg on close', inject(function($ionicPlatform) {
+    var openAmount = 0;
+    var deregSpy = jasmine.createSpy('deregister');
+    spyOn($ionicPlatform, 'registerBackButtonAction').andReturn(deregSpy);
+
+    var ctrl = setup();
+    spyOn(ctrl, 'getOpenAmount').andCallFake(function() { return openAmount; });
+
+    expect($ionicPlatform.registerBackButtonAction).not.toHaveBeenCalled();
+    openAmount = 1;
+    ctrl.$scope.$apply();
+    expect($ionicPlatform.registerBackButtonAction).toHaveBeenCalledWith(
+      jasmine.any(Function),
+      PLATFORM_BACK_BUTTON_PRIORITY_SIDE_MENU
+    );
+    expect(deregSpy).not.toHaveBeenCalled();
+    openAmount = 0;
+    ctrl.$scope.$apply();
+    expect(deregSpy).toHaveBeenCalled();
+  }));
+});