1) This fits with our splitting the old Buttons Window into Tools and Properties
2) The name Buttons Window doesn't communicate what it is for, only that it includes buttons. Of course, most other editors include a fair amount of 'buttons' too.
3) A 'button' is not usually what you'd associate with a slider, number field, checkbox or menu. Really there are hardly any true buttons in this window space.
Also added some notifiers to sequencer RNA, though there seems to be some refresh errors in the image preview area.
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