Support for Variable Trees in Metamodel

This is Herb's story.

1. Support added for variable trees in the Metamodel component. 
 (Only supports one level tree depth)

2. Config checks added to MetaModel

3. Dictionaries of slots are now supported on the Slot panel in the GUI. 

4. The slot figures are now sized based on the length of their name.

5. If Includes or Excludes are changed, the slot sizing doesn't work because you canna get the size from a hidden element. When this is detected, we revert to a default width of 100 pixels.

6. Support for arguments added to fill_from_library function in the Slot PageObject.