Support hierarchical display of array values

It is possible to enter arrays and hash arrays in the watch list to show their values, keys, and size, e.g. `${hasharray[@]}`, `${!hasharray[@]}`, and `${#hasharray[@]}`. Currently, values and keys are display as one string. It would be great if array variables were recognized as arrays and one could "open" the in the watch list to show their elements one by one.