Add structured errors and callbacks. Now sends candidates.
Add structured errors and callbacks. Now sends candidates.

williamboman/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,williamboman/matrix-js-sdk,williamboman/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk,krombel/matrix-js-sdk,matrix-org/matrix-js-sdk