BHV-10114 Updata metrics after collection changed.

Especially in dataGridList, after model added or removed then HandleSpotlightFocus() is not working well.
When you press down from bottom item, it should scroll a single row.
However after some models are added, it scrolls two rows and you can see spotlight focus.
(It is out of view port)

When collection is changed, list.indexBoundFirstRow and list.indexBoundLastRow should be updated too.
To resolve this, I calls updateMetrics when model is added or removed

Enyo-DCO-1.1-Signed-off-by: David Um david.um@lge.com
Hi @DavidUM, could we instead implement `modelsAdded` and `modelsRemoved` in enyo's VerticalGridDelegate? This way we guarantee the updating of the index bounds always happens when appropriate i.e. models are added/removed for a non-Moonstone control utilizing `enyo.DataGridList`.