Add merge() and parent() utils; move Extendable to go.components.structures
Add Lookup structure
Remove go.utils.parent()
Implement basic go.components.structures.ViewCollection
Add test for ViewCollection.destroy() to check if a view's .destroy() is called if it exists
Removed ViewCollection.render()'s removing of 'dead' views and adding of 'new' views. It is superfluous since we add/remove views on add/removes to the collection of models
Unset properties should return undefined
Add views on collection adds and removes
Small bit of code cleanup for ViewCollection
Make ViewCollection adding and removing internal