[wip] introduce POJOs API in core and move proto stuff to dedicated module

This compiles but is incomplete and certainly does not pass any test.
implement serialization of JournalEntry for RaftLog

* use plain old Java serialization
implement properly equals/hashcode/toString
convert from POJOs to Protos and back
added minimal package documentation
remove dependency on protoc and protobuf
handle request vote message through POST endpoint
handle append entries message through POST endpoint
implement client for RequestVote
implement client for AppendEntries
move tests to correct package
expose commit operation on server
configure a cluster with HTTP transport
creates an HTTP Raft client
retrieve current state of Raft service
add generic type to future returned by init
replica' toString is its raw URI

* The log store the replica information extracted from toString and pass it back to ClusterConfig to find a replica
move prober utility to core
explicitly initialize raft resource and do not return anything on commit

* returning Object on commit poses some serialization issues
completed integration test with only HTTP components

* tests is verbose and redundant with NettyRaftServiceTest, some stuff could be factorized especially the cluster configuration which could be made more generic