ENYO-654: Allow panels handle to show when panels are hidden.

### Issue
This is a regression from https://github.com/enyojs/moonstone/commit/027f64. Now that we are properly calling the super method for `getAbsoluteShowing`, whenever we attempt to spot the handle, we are examining the absolute showing state of the parent of the handle, which is the panels control that is not currently showing. Previously, this would be incorrectly skipped in the hierarchy and the parent of the panels control would be examined, which would be the sample itself, which is showing.

### Fix
We are now overriding `getAbsoluteShowing` for the handle specifically, via a separate kind. Additionally, I didn't see any reason to keep our override of `getAbsoluteShowing` in `moon.Panels` anymore (I believe it was originally put into place to support this unique case with the handle) as I couldn't find any calls to `getAbsoluteShowing()` or `getAbsoluteShowing(false)`, just calls to `getAbsoluteShowing(true)`, which can effectively be handled by the base kind's implementation of `getAbsoluteShowing`.

Enyo-DCO-1.1-Signed-off-by: Aaron Tam <aaron.tam@lge.com>