Move unix_time(), id_cpy()/id_eq(), is_timeout()  to util.*

unix_time():
- returns local value for current epoch
- value is updated explicitly with unix_time_update() called at new_DHT()/doMessenger()/do_DHT()

is_timeout():
- uses the local value for current epoch

id_cpy()/id_eq() => id_copy()/id_equal():
- centralized duplicate definitions
- replaced (most) memcpy()/memcmp() of (*, *, CLIENT_ID_SIZE) with id_copy()/id_equal()
Merge remote-tracking branch 'upstream/master' into cleanup_unix_time_id_eq_cpy_is_timeout

Conflicts:
	toxcore/net_crypto.c
For security reasons, keep memcpy's and memcmp's in crypto functions.
All modules using unix_time should run unix_time_update()
Update time before running functions for recieved packets.