Jewel List scrollToIndex Not Working Properly

Two problems:

1) I can confirm that scrollToIndex on a Jewel List works correctly under normal circumstances. I can also confirm that when the List is setup with a HorizontalLayout bead, or a TileLayout bead, scrollToIndex does nothing. So in the following example, scrollToIndex will fail:

```
photoList.scrollToIndex(30);

```

It will also fail when set up like this:

```
photoList.scrollToIndex(30);

```

2) You cannot scroll a List using the mouse wheel when the layout is set to HorizontalLayout

Start by reproducing the two cases in the issue: Jewel List scrollToIndex with HorizontalLayout and TileLayout, then test mouse-wheel scrolling with HorizontalLayout. Done means scrollToIndex reaches the requested item with both layouts and mouse-wheel scrolling works for a horizontally laid-out List.

Written by the indexing model from the issue text.