ui: introduce use of selectors for EntityList

[aspiers]

Description

The new EntityList component introduced by #167 has pretty terrible performance, but only half (roughly) of this is the slowness of fetching data from the API. The rest is mostly the cost of constructing the large entity list. We can do an initial optimisation on this by constructing the list using selectors, and then memoizing the results using the reselect selector library for Redux.

Comments, Questions and Considerations

#167 already ensures that the list of entities is only fetched from the API the first time it's needed, so we only need to optimise the rendering.

Plenty of nice HOWTOs are available for this, e.g.

• http://blog.rangle.io/react-and-redux-performance-with-reselect/

Acceptance Criteria

This story can be considered done when the following acceptance tests
are satisfied:

Given a MUTI interface already showing a long entity list

When I switch away from the entity list and back to it again

Then it renders quickly without recalculating the HTML for the whole list.