This should provide acceptable memory usage and database locking
granularity, while making subscription and transport updates large
enough for the incremental update issue to be kicked into the long
grass.
Removed awareness of the serialisation format from the protocol
component wherever possible, and added tests to ensure that the
constants defined in the protocol package's API are compatible with
the serialisation format.
database - unlike transport properties, these are not shared with
contacts. For example, when using email as a transport, the address
for sending and receiving emails would be a transport property, while
the username and password for the email server would be transport
configuration details. Transport plugins can update their
configuration details atomically.
Also clarified the terminology for transport and subscription updates.
