[TIMOB-8221] MobileWeb: Create an "inner" or "hidden" control concept

Many of our controls are created by assembling other controls. While this is great from a reuse standpoint, it makes the element graph look different than the user expects. This also affects the "source" object in UI events that can be unexpected from the user's perspective. We need to create a property of some sort that tells a control it is one of these hidden controls and needs to hide itself from the user. This affects the "children" property. Hidden children should NOT be returned in the array of children. We need to add some general helpers to the View subclass.