Gk browser editing arrays

Makes it possible to 

*add or delete one or more object in a table
*create and insert one or more objects at selected rows in array
*remove one or more objects from array at selected rows
*ditto plus delete
*move one or more objects within an array by dragging

The created objects are filled with default values set in my code. Should probably check if defaults exist for the classes and use that when possible. The logic for letting the browser produce the default values is that the user might want to customise this, and the browser user might not have access to the model classes.

I know this is a big merge, but there isn't really any good way to split it into smaller merges. I will provide a  flow chart for the actions, since each interaction involves around half a dozen methods in 3 or 4 classes.
I'm only storing the row indices, and they are only used in the case where rows are moved within an array property. In other cases (in a later PR) I store references to the objects being dragged.