This commit adds notifications for focus and blur on CPTokenField.
Attached is a modified Manual CPTokenFieldTest that observes these notifications.
Fixes#1396
In Aristo 2, the token field tokens would always show the close button, and make a big space for it.
This change makes it so that when the delete button, and the new disclosure button, are hidden, which is most of the time, the token doesn't look like it has a big empty hole on the right side.
Disclosure arrow behaves like in Cocoa: it shows on hover and if clicked displays the token specific menu.
This change also removes the delete button by default. The delete button can be enabled with `[tokenField setButtonType: CPTokenFieldDeleteButtonType]`.
This change implements support for the CPTokenField delegate method `tokenField:menuForRepresentedObject:` (and the associated `tokenField:hasMenuForRepresentedObject:`).
Note: this replaces the previous non Cocoa behaviour where the token field would grow height-wise with new tokens. This behaviour can still be useful, as seen in Apple Mail, but it will now require the user to subclass CPTokenField, override layoutSubview and set the frame size to the size of the scroll view's document view.