Option to also clear instance storage when using admin/instance/remove

[maackle]

admin/instance/remove could take an extra boolean clean parameter, which if true, also deletes the instance's storage.

Alternatively, add the option to admin/instance/add (perhaps calling it replace in this case), which will cause storage to be cleared if it already exists.

Use case:

During development, let's say I have been testing my DNA with a particular instance. Now I want to update the DNA. If I keep the same instance ID, it will attempt to use the old storage, since storage directories are named by the instance ID.