After rebasing the stack on master now both web and native started using the olm methods to sign messages. Because of that this diff introduces a new method to olmAPI -> signMessage. On native it's just an alias for commCoreModule implementation and on web it proxies to a simple signing function on worker.

Depends on D11373

Called olmApi.signMessage on native. Exported the pickled cryptostore from native and imported it on web. Called olmApi.signMessage on web. Made sure that the outputs matched (for the same input).