Add a podspec for JTTableViewGestureRecognizer

Just a podspec to use `JTTableViewGestureRecognizer` more easily via CocoaPods.

```ruby
pod 'JTTableViewGestureRecognizer', :git => "https://github.com/jamztang/JTGestureBasedTableViewDemo.git"
```

Please add a tag which the podspec requires. Thanks for creating this demo!