Allows change/changing notifications to be delayed

Simple API:

using (reactiveObject.DelayChangeNotifications()) {
  // change a bunch of properties
} // notifications will fire
address comments
Merge branch 'rxui6-master' into add_delay_change_notifications_to_RO
Merge branch 'rxui6-master' into add_delay_change_notifications_to_RO
boolean logic is tough stuff, so many different possible options!
Add a test for delaying notifications
Fix activation when IsHitTestVisible does not change.
Merge pull request #646 from reactiveui/activation-hittest-fix

Fix activation when IsHitTestVisible does not change.
Add a Xamarin.Forms scheduler
Merge branch 'rxui6-master' of github.com:reactiveui/ReactiveUI into rxui6-master
Omgggggg
Test recursive acquiring the delay
Close the window as soon as we start delaying notifications
Make sure we only kick things off on first delay
Merge branch 'add_delay_change_notifications_to_RO' into rxui6-master
Fix incorrect passing of expression.
Merge pull request #648 from reactiveui/fix-onewaybind-bug

Fix incorrect passing of Lambda expression.
Fixes a bug where if:

Object.Prop1 changes
Object.Prop1 is being listened for changes, and when Prop1 changes, it causes Prop2 to change
Object.Prop2 change listener doesn't fire properly (it is caught in the buffer)

This is because the way Buffer is implemented internally, it Nexts out the buffer, then re-grabs the Close observable, so any changes created during that window are stuck until the buffer gets closed next time.
Much cleaner fix, that still allows the publish/refcount
Merge pull request #649 from reactiveui/fix_nested_object_change

Fix nested object change