This adds individual modules for caching sessions (for now only OlmSessions) and the decryption routine for events encrypted using m.olm.v1.curve25519-aes-sha2.
It refactors code for managing blocker IDs into its own module, which could also be used by the client.
After uploading OTKs they are now marked as published for the module's own OlmAccount.
Closes #11 (closed)