Accessibility improvements

[tomgayler-unbxd]

Based on work by DEFRA into how to make maps more accessible I have reviewed their guidance (https://github.com/DEFRA/design/wiki/Interactive-maps) and considered what actions we could take to improve the maps in RIPA-BoPS.

The list of findings and action items is here - https://docs.google.com/document/d/1jFdJjYQOP5DQs5ox1lAgzV2Gfpm4qDalDCVbZ_9PxpE/edit?usp=sharing