Group chat: Add a nickname message. Remove strange default nickname. (Seriously...)

group_chats.*:
- group_send_nick() to send own name
- setnick() to store a received name

Messenger.c:
- group_send_nick() before group_sendmessage() (in regular intervals, to inform new peers)

nTox.c:
- print_groupmessage(): on error or on a name of length zero the result of tox_group_peername() isn't null-terminated, catch that
Merge branch 'group_peername' of https://github.com/FullName/ProjectTox-Core into FullName-group_peername
Cleaned up the code.
Add a "conversation mode", where you set your conversation partner once and then all non-commands are sent as message to them.
/cf # rsp. /cg # sets, /cr resets target

Also reformatted display of sent group message slightly to look less beta-ish.
Then using "#<num>" for group number vs. "<num>" for friend/peer numbers.
Also changed to a slightly different message on people without name.
IPv6 address of ::1 is local.
On replacing a client with another, clear the stale association.
Also check both associations for timeout, not just the incoming one.

Also removed client_in_list(): static & unused.
Merge pull request #647 from FullName/ntox-conversations

Add a "conversation mode", where you set your conversation partner once ...
Merge pull request #648 from FullName/LAN_ip-ip6-loopback-is-local

IPv6 address of ::1 is local.
Wrapping: Expanded space of output to be a bit larger than input. Basic wrap(): Embed continuation markers if there's enough space.
Merge pull request #649 from FullName/DHT-client_id-change-wipe-other-address

On replacing a client with another, clear the stale association.
Merge pull request #651 from FullName/ntox-wrap-basic-with-continuation

Basic wrap(): Embed continuation markers if there's enough space.
Send our name when someone new joins the group chat.
Fixed build error on windows.
Tolerate instable connectivity: if *all* set close nodes are in terminal timeout (KILL_NODE_TIMEOUT), reset them all to BAD_NODE_TIMEOUT.
That keeps the client trying to at least ping the nodes in the hopes of the connection coming back up.
Fixed segfault.
Merge pull request #652 from FullName/reset_on_long_timeout

Tolerate instable connectivity.