Nut cannot be controlled if nut trap strips

[tareko]

Describe the bug
In the event of a failure of the nut trap, there is no 'backup' mode for removing the device, resulting in a situation where the device has to be destroyed while still on the patient to be removed.

Expected behavior
Even when the nut trap fails, there should be a graceful way to remove the nut.

Failure Mode
The nut cannot be removed when the nut trap is stripped or fails.

Effect
When the nut cannot be removed, the device is stuck on the patient and more drastic efforts have to be taken to remove the device.

Cause
The nut trap completely encloses the nut.

Mitigation / Control
Cut the nut trap height in half to expose some of the nut.

[tareko]

This issue is related to #24

[jenwilsonglia]

In extensive tests, even when the nut is released from the stripped nut trap, the nut cannot be loosened from the bolt due to the threads being deformed.

[tareko]

Another mitigation is to always ensure that the nut trap is used for the bolt head, not the nut. This allows another surface that can be gripped in the event of a loss of control like this.

At the moment, two mitigations:

1. Nut trap height is cut in half.
2. Nut trap is used for bolt head, not nut.

[jenwilsonglia]

Changing the name of "nut trap" to something like "bolt head holder" makes sense for the user instructions now that we are mitigating this problem by using the bolt head in this space that was the hex shaped nut trap, rather than using it for the nut.