materialisation: Add new message fields.

Added MessageAction enum to represent different message actions, and mapped action numbers to these enums.
Added `serial` to the message, this is the unique serial (including index) of the message.

Added the following fields related to message annotations
- `refSerial`
- `refType`
Added the following fields related to message edits/deletes
- `operation`
- `editedAt`
- `deletedAt`