Modified AbstractStatefulStyle to accept an observable list of dependencies instead of controlling it directly via methods in AbstractStatefulStyle.
Moved the controllability of the state of an AbstractInternallyStatefulStyle outside it.  It now accepts an observable set of styles (controlled elsewhere) and does not have modifier methods for this set.
Accidentally did some work twice.  Converted styles to accept observable collections of dependencies here, but then forgot I'll modified them to accept external states as well, so I redid that and now having to stomp on that work.

Merge branch 'feature-Spinner' of github.com:Updownquark/MUIS into feature-Spinner

Conflicts:
	projects/MUIS/src/main/java/org/muis/core/model/AbstractSelectableDocumentModel.java
	projects/MUIS/src/main/java/org/muis/core/style/attach/ElementHeirStyle.java
	projects/MUIS/src/main/java/org/muis/core/style/attach/ElementSelfStyle.java
	projects/MUIS/src/main/java/org/muis/core/style/attach/ElementStyle.java
	projects/MUIS/src/main/java/org/muis/core/style/stateful/AbstractInternallyStatefulStyle.java
Added a unit test class for styles.  Empty at the moment except for stub methods.