Feature: Add a WarningPanel as an alternative to the EntityIncidentCard

[xNok]

We ideally wanted to know when landing on an entity page if it was affected by an incident. However, we found that the EntityIncidentCard was taking up too much space. Instead, we think a WarningPanel would be a much better way to inform users of Ongoing incidents.

Other changes:

• Set up the dev server; this allows people to run yarn start and see what the different components of the plugin look like.