DAE: Apply veto changes whilst Fermi crate disconnected

As a Merlin instrument scientist, I would like to be able to change vetos from the GUI while the Fermi crate is disconnected so that I can continue to apply changes to the DAE whilst operating with a white beam.

On discussion with Helen, in SECI it used to be that you could apply changes to vetos whilst the fermi crate was disconnected. In IBEX, she describes that the veto panel in DAE/Experiment setup and the Apply changes button are greyed out when the crate is off. Please can the SECI behaviour be available in IBEX

## Acceptance criteria

- [ ] When the DAE registers that the Fermi Crate is disconnected, the other veto controls are still enabled in the client