sample stage opi: show soft limits

As a user I would like the [sample stage OPI](https://github.com/ISISComputingGroup/ibex_gui/blob/master/base/uk.ac.stfc.isis.ibex.opis/resources/sample_stack/sample_stack.opi) to show soft limits of the motor it's controlling. This is because if they are set narrow a user might not necessarily know that their motor has hit a soft limit and that's why it won't move.

### acceptance criteria
- [ ] sample stage OPI shows soft limits (`LLM`, `HLM` on the [motor record](https://epics.anl.gov/bcda/synApps/motor/motorRecord.html)) of the motors shown on the OPI.