Bump matrix-js-sdk to 0.8.0+

The matrix-js-sdk has introduced breaking changes in 0.8.0 to the crypto code. Our current approach of doing a state sync, then stopping the client, then restarting it with the wanted sync token does no longer work with the new matrix-js-sdk as it destroys the matrixStore the crypto code relies on.

We need to redo this part - maybe it is possible to keep the client running and to update the sync token while it runs. This would remove the stop / restart step and should work with the new crypto code. We also need to introduce the async initCrypto call (as given in the changelog for 0.8.0).