Automatically handle when devices are inside the brain

[kjy5]

Automatically detect when a device is inside the brain and enable the appropriate movement restricting flags (like inside_brain). Extracted from #24

• Measure pressure to automatically detect if inside brain
• Set flags
• Document

[kjy5]

Could be done via connection with trajectory planner. When probe is driven through the surface, send signal to enable axis lock

[kjy5]

Handled by #40 and maybe the camera system at the Allen Institute