More functionality added to the ExpressionCapture System

Nothing really tested, just blocked out more critical functionality. Icons
built for the expression drop system. Button added to the UI for the
ExpressionStateNode. Basic drop is working, but need to properly consider
the process drop to setup a name and add appropriate Expression data.
ExpressionFaceNode creation and deletion complete

The basics of dragging in a new Expression and deleting an expression is
now implemented. Names are checked with the ExpressionCaptureProcessor to
make sure that they are unique, when being added to a scene.

Nothing tested for actually storing node positions etc.
Expression Capture System is working! No store/Read

The capture system is now full implemented mainly through the
ExpressionCaptureProcessor.processCombinedExpressions method. This method
looks at the ExpressionFaceState in the self.faceSnapShot, and compares
each controller that it finds to the positioning in that faceState. From
there the total difference can be calculated. The correct percentage is
taken of this, and stored as a delta in the faceSnapShot
ExpressionItemStates. Once all the deltas have been added up for all the
expressions, then the final position of the nodes can be calculated, and
the nodes are placed there.

Setting a new faceSnapShot resets all the sliders on all the
ExpressionStateNodes to zero, so no expression is contributing anything.
From there, any expression can be dialled in....