moved stuff that belongs into ping.[ch] there

DHT.*, ping.*:
- moved stuff from struct DHT into struct PING: toping, last_toping
- moved functions add_toping(), do_toping()
- made id_closest() publicly accessible
- send_ping_request(): killed (Net_Crypto *c) parameter in favor of copying it into (PING *) on new_ping()

group_chats.c:
- killed local 1:1 copy in favor of DHT.c::id_closest()
Fixed windows build.
Possible bug fixed.
Possibly fixed the weird disconnecting/reconnecting bug.
Merge branch 'master' of https://github.com/irungentoo/ProjectTox-Core
Merge pull request #596 from FullName/ping.moveandclean

moved stuff that belongs into ping.[ch] there
Fixed possible bug.
Fixed bug where hole punching was attempted even though the
clients were connected.

Increased the number of ports tried per interval of time.

Also astyled the files.