`scrolling` event for `ScrollableViews`.

[TC-827] iOS implementation as well as documentation and testing for an event
`scrolling` emitted from `ScrollableViews` during scrolling.
`ScrollableView` event renames.

Renamed the following events of `ScrollableView`:
 * `scroll` → `scrollEnd`
 * `scrolling` -> `scroll`
Fixing tests to reflect event renames.
Fixing docs to reflect event renames.
Moving & fixing  `Scrollable` tests.

Moved from `iphone/iphone.ui.js` to `ui.controls.js` because these
events will be supported on Android as well.
Working the `ScrollableView` events (Android).

Renamed the `scroll` event to `dragEnd`.  Implemented the correct
`scroll` event and the `scrollEnd` event.
Fixing `ScrollableView` docs.

Adding `dragEnd` event on Android and adding Android to the
compatibility list for the `scroll` and `scrollEnd` events.
Merge branch 'TC-827-scrolling-event' of https://github.com/russfrank/titanium_mobile into russfrank-TC-827-scrolling-event
Fire a scroll event if user taps the status bar ("scroll to top"). iOS-only AFAIK
Fixing spacing in `ScrollableView.yml`.
Updating comment in test to reflect new event name
Correcting scroll events for ScrollableView.

Instead of using the `onPageSelected` handler of our
`ViewPager.SimpleOnPageChangeListener` to fire `dragEnd` events, use the
`onPageScrollStateChanged`.  This will properly fire `dragEnd` events
even when we haven't actually completed a scroll to another view.

Instead of using the `position` parameter passed to the `onPageScrolled`
handler of our `ViewPager.SimpleOnPageChangeListener` alone to determine the
current index, use it in combination with the `positionOffset`;
rounding.  This way, we get a value of 2 for the index when we are more
than halfway scrolled onto page 2.
Relaxing drillbit test for Scrollable events.
Doc fixes for `ScrollableView`.

Added "since" for the modified events in `ScrollableView`.  Tried to
clarify language in some places.
Fixing paging indicators & edge case of scrollEnd.

The paging indicators broke because I mistakenly made a property
`mCurIndex` of the page change listener for the `ViewPager`.  Thus, the
indicators didn't know what page to go to when clicked.  I was also
checking to see if they needed to be shown at the wrong time; this has
been corrected by calling `showPager()` whenever we fire a `scrollEnd`.

This commit also introduces a hacky fix for an edge case of `scrollEnd`.
If the user drags the view and manually settles it on another view, the
`onPageScrollStateChanged` handler is never called.  So, we use the
`onPageSelected` handler in this case; but only if a `dragEnd` event
wasn't fired beforehand.
Making tests even more lenient for Android.
Documentation touch-ups for `ScrollableView`.
Not firing scrollEnd when mCurIndex is -1.
[TIMOB-9084]Make validation methods static
[TIMOB-9084]Refactor for static method names