riak_repl_aae_sink should be a gen_fsm like riak_repl_aae_source

[bsparrow435]

I don't see any reason why riak_repl_aae_sink and riak_repl_aae_source use different behaviors. It would make sense to have one common worker behavior for these modules and gen_fsm seems the logical choice given the type of work they are doing.

[cmeiklejohn]

Scheduled for 2.1, as part of work to improve AAE-based replication.