Switch from a FakeStore to a Vuex store with a history plugin

Now that we can run tests on components directly, it should also be possible to replace the FakeStore with a Vuex.Store. The store however lacks a history feature (only provided by the Vue devtools extension); we can add it using a store plugin that subscribes to both actions and mutations. To also have nicer errors displayed during tests, we should bump to Vuex >=3.4 to get a error handler on subscribeAction.