OpRequest: move method implementations into cc

I need to remove the osd_types.h include.

Signed-off-by: Samuel Just <sam.just@inktank.com>
osd_types,OpRequest: move osd_req_id into OpRequest

This was I can have OpRequest included from osd_types.h.

Signed-off-by: Samuel Just <sam.just@inktank.com>
ReplicatedPG,osd_types: move rw tracking from its own map to ObjectContext

Signed-off-by: Samuel Just <sam.just@inktank.com>