AMQP status updates with state "gone" should not delete the IC in the database

/cc @irismarie

Iris noticed that by restarting VILLAScontroller we create a new ICs everytime because the backend currently deletes the ICs in the DB if it receives an update with state == gone.

I propose to use two states to handle IC shutdown and deletion:

state == gone: VILLAScontroller which manages this IC has been terminated. The IC is currently unsusable until the controller starts again. We should retain the IC in the DB in order to avoid breaking any references to IC configurations.
state == deleted: This is the last update of an IC before it gets deleted by its manager / AMQP delete action. The IC will not be used anymore. It should be deleted from the DB.

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