Eliminate redundant logs

There are several messages that are very repetitive and no very useful, like:

• This one is really not necessary:

  ucode=1015, message=Document already under treatment

• This one either:

  ucode=2023, message=Peer document already known

• Same:

  info: ⬇ PEER 69MN2qvK
  info: ✘ PEER 69MN2qvK

  For peers, we could just remove the incoming document logging.

• Too much spam:

  2017-10-08T16:25:30+02:00 - info: POST Peer HmH5beJqKG#58980
  2017-10-08T16:25:30+02:00 - debug: --> new Peer to be sent to 10 peer(s)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer DfjVNNn7JW [member] (duniter.lamessen.me:80)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer CGnyAAKDSK [member] (185.167.16.19:10901)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer 3wdDzBz18m [member] (g1.smyds.net:443)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer gtAf2Rm7cu [member] (duniter.charleshd.com:80)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer Do99s6wQR2 [member] (g1.citiz-network.org:16262)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer H1yTj77m94 [member] (duniter.jowe.fr:443)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer GYEtpPnK2N [------] (duniter.laurent-st-math.fr:80)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer ZPVG2pn8B9 [------] (duniter.adn.life:10901)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer EZBtAeBmW2 [------] (g1.monnaielibreoccitanie.org:10901)
  2017-10-08T16:25:30+02:00 - debug:  `--> to peer 4364zZpziQ [------] (duniter.silibre.com:80)

  Which could be reduced to:

  2017-10-08T16:25:30+02:00 - info: POST Peer HmH5beJqKG#58980 to 10 peer(s)

mentioned in commit f7df3868