Reconcile I22 and I03 DCMs

As a developer I would like to work with a minimal number of `DCM` classes.

Currently the PV naming conventions vary across beamlines, even when the hardware configuration is relatively similar.
In the case of I22 and I03, the DCMs are quite similar. According to @JamesOHeaDLS:

> The main difference is that I03 only has roll and pitch on one of their crystals, whereas I22 has roll and pitch on both their first and second crystals

Which suggests that the PVs could at least adopt the same naming _conventions_, even if one DCM has extra motors, and we could have a shared base class.

## Acceptance Criteria
* One `DCM` base class
* I03 and I22 implementations with only the extra I22 motor added