Create EntityFieldKeys and EntityFieldType
There's know EntityFieldKeys and EntityFieldType to store the keys and type of a field. These elements are owned by the EntityField element and is displayed as children. EntityField still stores the name of the field.
Fixes #1 (closed) - Since these are all separate elements, Apollon will serialize them when saving the diagram.
Known issues:
- The field doesn't display in the sidebar with the entity
- Creating the keys and type elements is done when adding a new field element, but it's done in a separate action in the redux stack, so it's possible to undo and leave a field with no key or type
Otherwise it seems like this will give us a fully functional ER diagram type, minus some minor bugs.