feat(tabs): makes swipe gestures on the content area opt-in

Closes #2331

BREAKING CHANGE: Tabs will now require the `md-swipe-content` attribute in order to enable swipe gestures to change tabs in the content area.

src/components/tabs/js/tabsDirective.js

@@ -59,6 +59,7 @@
  * @param {boolean=} md-dynamic-height When enabled, the tab wrapper will resize based on the contents of the selected tab
  * @param {boolean=} md-center-tabs When enabled, tabs will be centered provided there is no need for pagination
  * @param {boolean=} md-no-pagination When enabled, pagination will remain off
+ * @param {boolean=} md-swipe-content When enabled, swipe gestures will be enabled for the content area to jump between tabs
  *
  * @usage
  * <hljs lang="html">
@@ -92,7 +93,8 @@ function MdTabs ($mdTheming, $mdUtil, $compile) {
       dynamicHeight: '=?mdDynamicHeight',
       centerTabs:    '=?mdCenterTabs',
       selectedIndex: '=?mdSelected',
-      stretchTabs:   '@?mdStretchTabs'
+      stretchTabs:   '@?mdStretchTabs',
+      swipeContent:  '=?mdSwipeContent'
     },
     template: function (element, attr) {
       attr["$mdTabsTemplate"] = element.html();
@@ -175,8 +177,8 @@ function MdTabs ($mdTheming, $mdUtil, $compile) {
               id="tab-content-{{tab.id}}"\
               role="tabpanel"\
               aria-labelledby="tab-item-{{tab.id}}"\
-              md-swipe-left="$mdTabsCtrl.incrementSelectedIndex(1)"\
-              md-swipe-right="$mdTabsCtrl.incrementSelectedIndex(-1)"\
+              md-swipe-left="swipeContent && $mdTabsCtrl.incrementSelectedIndex(1)"\
+              md-swipe-right="swipeContent && $mdTabsCtrl.incrementSelectedIndex(-1)"\
               ng-if="$mdTabsCtrl.hasContent"\
               ng-repeat="(index, tab) in $mdTabsCtrl.tabs" \
               md-template="tab.template"\