Added endpoint to deactivate an account

[BichraiX]

Added this endpoint from the spec : https://spec.matrix.org/v1.11/client-server-api/#post_matrixclientv3accountdeactivate

• Modified multiple files error sending to replace e/err by e/err.toString() so that the logger logs the error message received.
• Modified the SafeClientEvent class and tests to directly handle a ClientEvent instead of any object.
• Added TODOs in /register for the future and added feature to fill new database tables with device information.
• Refactored delete3pid function to be callable outside of the endpoint to delete a 3pid association.
• Moved /whoami tests to new file account.test.ts along with the new tests to /deactivate endpoint.
• Deactivate endpoint is not finished and requires implementing the /leave endpoint in the future.