feat: handle courseware paths more liberally (#395)

Valid courseware URLs currently include:
* /course/:courseId
* /course/:courseId/:sequenceId
* /course/:courseId/:sequenceId/:unitId

In this commit we add support for:
* /course/:courseId/:sectionId
* /course/:courseId/:sectionId/:unitId
* /course/:courseId/:unitId

All URL forms still redirect to:
  /course/:courseId/:sequenceId/:unitId

See ADR #8 for more context.

All changes:
* refactor: allow courseBlocks factory to build multiple sections
* refactor: make CoursewareContainer tests less brittle & stateful
* feat: handle courseware paths more liberally
* refactor: reorder, rename, & comment redirection functions

TNL-7796

src/setupTest.js

@@ -132,7 +132,7 @@ export async function initializeTestStore(options = {}, overrideStore = true) {
   axiosMock.reset();
 
   const {
-    courseBlocks, sequenceBlock, courseMetadata, sequenceMetadata,
+    courseBlocks, sequenceBlocks, courseMetadata, sequenceMetadata,
   } = buildSimpleCourseAndSequenceMetadata(options);
 
   let forbiddenCourseUrl = `${getConfig().LMS_BASE_URL}/api/courseware/course/${courseMetadata.id}`;
@@ -153,7 +153,7 @@ export async function initializeTestStore(options = {}, overrideStore = true) {
   !options.excludeFetchCourse && await executeThunk(fetchCourse(courseMetadata.id), store.dispatch);
 
   if (!options.excludeFetchSequence) {
-    await Promise.all(sequenceBlock
+    await Promise.all(sequenceBlocks
       .map(block => executeThunk(fetchSequence(block.id), store.dispatch)));
   }