* Rewrite `deleteAccountData` test
use fetch-mock rather than whatever this was
* `MatrixClient.setAccountData`: await remote echo
Wait for the echo to come back from the server before we assume the account
data has been successfully set
* Update integration tests
Fix up the integ tests which call `setAccountData` and now need a sync
response.
* Address review comment
* Rust-crypto: fix `bootstrapCrossSigning` on second call
Currently, `bootstrapCrossSigning` raises an exception if it is called a second
time before secret storage is set up. It is easily fixed by checking that 4S is
set up before trying to export to 4S.
Also a few logging fixes while we're in the area.
* Factor out an `AccountDataAccumulator`
* Another test for bootstrapCrossSigning
