Group chat peers now tell others when they quit.

Also increased ping timeout.
Speed up group chat bootstrapping by a bit.
Added function to get the number of peers and list of names for group chats.
Added callback that tells you when the peer name list of a group chat changes.
Kill_messenger now kills group chats.
Fixed bug with group chats.
group_namelistchange(): for ui reasons, divulge the peernumber and the nature of the change (add, del, name change).

tox.*, Messenger.*, group_chats.*:
- expand interface of callback by peernumber/change

groupchats.c:
- call callback in addpeer/delpeer/setnick with peernumber and flag

nTox.c:
- print_groupchatpeers(): print as many names on a line as possible, not one peer per line
- print_groupnamelistchange(): only print the change, if possible (i.e. "new peer", "peer's new name")
- added command "/p" to print the list of peers
Fixed possible build problem.
Mimic more exactly what delpeer() does in the callback.
If the deleted peer wasn't last, send a name-change update for the overwritten peer.
setnick(): don't callback when an identical nickname is set again
Merge pull request #663 from FullName/peerchange-detail

group_namelistchange(): for gui reasons, divulge peernumber and change type
Behaviour changes for the group chat callback.
Print a more detailed message on CHAT_CHANGE_PEER_DEL, so a user isn't confounded by the change of peer numbers.

On deleting the last peer, it's just a delete.
On deleting any other peer, the last peer is moved into that space, gaining a different number.
Print that detail where appropriate.
Merge pull request #665 from FullName/peerdel-ntox-feedback

Print a more detailed message on CHAT_CHANGE_PEER_DEL, so a user isn't confounded...
Friend requests from friends are now discarded.
Various changes to nTox including a potential crash (also possible from remote!), and a tiny change to toxcore.

Crash stuff:

nTox.c:
- do_refresh(): avoid crashes (input a "%" and the client goes "boom!", send someone a string with embedded "%" and see him blow up...)

Other stuff:

toxcore: tox.h (doc.)/network.c (code):
- networking_wait_prepare(): return -1 if lenptr was NULL and therefore not settable

nTox.c:
- fraddr_to_str(): function to convert a TOX_FRIEND_ADDRESS into a segmented (and therefore line-breakable) string
- print_friendlist(): print index of friend on name line, print id on 2nd line
- command /f: skip spaces (and +) inside a friend id
- command /r (new): "/r #" to remove a friend
- main(): reduce cpu consumption if we're not currently sending files
Fixed ghost peer problem.
30 seconds is way too long.
Merge pull request #666 from FullName/nTox-various

Various changes to nTox including a potential crash (also possible from remote!)...