Made changefeed::client_addr_t and changefeed::server_addr_t.
Updated generate_rpc_templates.py to actually generate recent changes in mailbox/typed.hpp.
Made a separate rpc/mailbox/addr.hpp header.
Improved includes a tad.
Added changefeed_types.hpp header.
Made protocol.hpp include changefeed_types.hpp.
Added mailbox_addr_t<>::mailbox_type.
Made registration_metadata.hpp not include typed.hpp.
Reduced inclusions of rpc/mailbox/typed.hpp a bit.