Refactoring data management. Using context now.

Ripped out the subSection and unit code for the moment to refactor it to use the context - breadcrumbs is currently working with it, though.

src/learning-sequence/hooks.js

@@ -0,0 +1,39 @@
+import { useContext, useMemo, useState, useEffect } from 'react';
+import { AppContext } from '@edx/frontend-platform/react';
+
+import CourseStructureContext from './CourseStructureContext';
+import { findBlockAncestry, getCourseBlocks, createBlocksMap } from './api';
+
+export function useBlockAncestry(blockId) {
+  const { blocks, loaded } = useContext(CourseStructureContext);
+  return useMemo(() => {
+    if (!loaded) {
+      return [];
+    }
+    return findBlockAncestry(
+      blocks,
+      blockId,
+    );
+  }, [blocks, blockId, loaded]);
+}
+
+export function useCourseStructure(courseId) {
+  const { authenticatedUser } = useContext(AppContext);
+
+  const [blocks, setBlocks] = useState({});
+  const [loaded, setLoaded] = useState(false);
+  const [courseBlockId, setCourseBlockId] = useState();
+
+  useEffect(() => {
+    setLoaded(false);
+    getCourseBlocks(courseId, authenticatedUser.username).then((blocksData) => {
+      setBlocks(createBlocksMap(blocksData.blocks));
+      setCourseBlockId(blocksData.root);
+      setLoaded(true);
+    });
+  }, [courseId]);
+
+  return {
+    blocks, loaded, courseBlockId,
+  };
+}