Updates to support tethering to a class
Support new function
Implement new function
Add methods to get a diagram's elements and get a unique element from unique ID
Add a function to set an element near another element
Re-work so that this state only moves the diagram panel around and swaps to a selected element state if an element is clicked. (No longer handles the selected element)
New state to handle elements after they've already been selected.
New class to handle data associated with tethering one element to another.