Bug 934209 - support multi-row for key popup.

Let's rename `AlternativesCharMenu` to either `AlternativesCharMenuView` or `AlternativesCharMenuRender` since it's part of the render or the future view classes.

The current names give me the assumption that it has a relationship with `AlternativesCharMenuManager` like `TargetHandlersManager` v.s. `XXXTargetHandlers`.