ENYO-286: moon.Scroller halts when content is focused

Due to a recent regression, moon.Scroller stops scrolling as soon
as an item inside it is focused.

This regression occurred because we started using
`onSpotlightFocused` and `onSpotlightBlur` events to detect when
focus entered / left the scroller; previously, we had used
`onSpotlightContainerEnter` and `onSpotlightContainerLeave`. In
making this change, we reused existing handlers for pointer-based
`enter` and `leave` events, but these handlers called
`setupBounds()`, which in turn invoked logic in `enyo.ScrollMath`
that caused scrolling to stop.

We now create a separate handler to deal with the Spotlight events,
which we ignore when in Pointer mode. As a bonus, we also replace
the call to `setupBounds()` in the `enter` handler and instead call
just the subroutines that we need to show / hide the pagination
controls.

These changes have been tested against all of the Moonstone
scroller samples.

Enyo-DCO-1.1-Signed-Off-By: Gray Norton (gray.norton@lge.com)
Merge pull request #1684 from enyojs/ENYO-286-graynorton

ENYO-286: moon.Scroller halts when content is focused

Reviewed-By: Aaron Tam (aaron.tam@lge.com)
Integrated-By: Ryan Duffy (ryan.duffy@lge.com)