ts: Improved error handling

package.json

src/api/ApiError.tsx

src/api/Backend.tsx

src/components/DefaultLayout.tsx

src/components/DownloadManager.tsx

src/components/FallbackErrorBoundary.tsx

src/components/OMConfigComponent.tsx

src/components/Player.tsx

src/misc/Util.tsx

src/pages/_app.tsx

src/pages/courses.tsx

src/pages/dynamic_course_listing.tsx

src/pages/dynamic_embed.tsx

src/pages/dynamic_player.tsx

src/pages/index.tsx

src/pages/internal/changelog.tsx

src/pages/internal/import.tsx

src/pages/internal/jobs/overview.tsx

src/pages/internal/sort/log.tsx

src/pages/internal/user.tsx