Reflectometry: Disallow moves when motors are disconnected

As a reflectometry scientist, when performing a move I do not want any part of the beamline to move if one or more motors involved in the move are disconnected.
If the server temporarily loses connection to some motors but not others and performs a move, we run the risk of crashing.

#### Acceptance Criteria:
1. If any motor is not connected in the moment a move is performed, the IOC should display an error and refuse to do a movement
1. Possibly the scientists will want an option for ignoring the error and proceeding at their own discretion, I will email them to find out.
1. When a successful move is performed, the error state is cleared.