tLN: Instantiate supervision with valid control block reference but no related subscriptions #79

If a supervision exists but has no associated subscriptions on an IED I allow it to be overwritten. But our current scl-lib API does not allow this and so my test fails.

The cause is:

https://github.com/OpenEnergyTools/scl-lib/blob/f67d73dd6c46a07ef0a19f1574f992c61358cc98/tLN/supervision/canInstantiateSubscriptionSupervision.ts#L152-L174

In the lower lines because there is a valid object reference I can't "remove" the supervision. I also don't have an option to force this.

Should we have:

• a check on whether there are any ExtRefs subscribed (is it OK to supervise an unused control block?)
• a "force" option here?
• Or, once we fix up the remove subscription supervision (to only removal the Val text content, see (tLN) Remove subscription supervision #18) should I just remove the supervision first?