TiAPI: Add "isTrusted" property to all events

Summary:
We should add an "isTrusted" boolean property to all events. This is a standard property available to web developers which is set to true if the event was made by user interaction. It is set false if the event was triggered programmatically. This is mostly useful UI based events.
https://developer.mozilla.org/docs/Web/API/Event/isTrusted

To-Do:
When an event is fired natively, the core code should add an "isTrusted" property if missing and default it to true. Events fired from JavaScript should default to false if the property is not defined.

We should set "isTrusted" to true/false directly for:

• Ti.UI.Picker "change"
• Ti.UI.RefreshControl "beginRefreshing"
• Ti.UI.SearchBar "change"
• Ti.UI.Switch "change"
• Ti.UI.Tab "selected" and "unselected"