Prevent pull-to-refresh from triggering while scrolling in a nested scrollable element on the page

[jayohms]

This fixes: #294

This prevents pull-to-refresh from being triggered when (potentially) nested scrolling within an element on the page that is using overflow-y: scroll or overflow-y: auto. To address this, the following item were added:

• On every touch start, check if the target element or any of its parent elements are scrollable. If any are scrollable, notify the TurboWebView that the currently touched element is scrollable.
• On every touch end, reset the internal state of the TurboWebView.
• Whenever the TurboSwipeRefreshLayout checks to see if its scrollable child can scroll up, check the state of the TurboWebView if a scrollable element is currently being touched.

[leonvogt]

Works like a charm, thanks @jayohms!