Moving courseStatus and courseId to “activeCourse” reducer.

Removing both from courseware and courseHome reducers.  This makes it easier for various portions of the app to find out what the current course is without being aware of which page is loaded.

In this MFE, we can basically always assume _some_ course is loaded.

docs/decisions/0004-model-store.md

@@ -4,6 +4,6 @@ Because we have a variety of models in this app (course, section, sequence, unit
 
 https://redux.js.org/faq/organizing-state#how-do-i-organize-nested-or-duplicate-data-in-my-state
 
-Different modules of the application maintain individual/lists of IDs that reference data stored in the model store.  These are akin to indices in a database, in that they allow you to quickly extract data from the model store without iteration or filtering.  
+Different modules of the application maintain individual/lists of IDs that reference data stored in the model store.  These are akin to indices in a database, in that they allow you to quickly extract data from the model store without iteration or filtering.
 
-A common pattern when loading data from an API endpoint is to use the model-store's redux actions (addModel, updateModel, etc.) to load the "models" themselves into the model store by ID, and then dispatch another action to save references elsewhere in the redux store to the data that was just added.  When adding courses, sequences, etc., to model-store, we also save the courseId and sequenceId in the 'courseware' part of redux.  This means the courseware React Components can extract the data from the model-store quickly by using the courseId as a key: `state.models.courses[state.courseware.courseId]`.  For an array, it iterates once over the ID list in order to extract the models from model-store.  This iteration is done when React components' re-render, and can be done less often through memoization as necessary.
+A common pattern when loading data from an API endpoint is to use the model-store's redux actions (addModel, updateModel, etc.) to load the "models" themselves into the model store by ID, and then dispatch another action to save references elsewhere in the redux store to the data that was just added.  When adding courses, sequences, etc., to model-store, we also save the courseId and sequenceId in the 'courseware' part of redux.  This means the courseware React Components can extract the data from the model-store quickly by using the courseId as a key: `state.models.courses[state.activeCourse.courseId]`.  For an array, it iterates once over the ID list in order to extract the models from model-store.  This iteration is done when React components' re-render, and can be done less often through memoization as necessary.