Refactor logging

- Conference logging now behaves the same as 1-on-1 chats: Instead
  of creating a new log file every time we restat the client
  we use the unique conference ID to keep track of path names.
  This also allows us to load history for saved groups on client startup

- Added a log init function / general code refactor.

- Fixed a bug that caused log files to be created even when logging
  is disabled.

src/friendlist.c

@@ -453,7 +453,9 @@ static void friendlist_onNickChange(ToxWindow *self, Tox *m, uint32_t num, const
     tox_self_get_address(m, (uint8_t *) myid);
 
     if (strcmp(oldname, newnamecpy) != 0) {
-        rename_logfile(oldname, newnamecpy, myid, Friends.list[num].pub_key, Friends.list[num].chatwin);
+        if (rename_logfile(oldname, newnamecpy, myid, Friends.list[num].pub_key, Friends.list[num].chatwin) != 0) {
+            fprintf(stderr, "Failed to rename friend chat log from `%s` to `%s`\n", oldname, newnamecpy);
+        }
     }
 
     sort_friendlist_index();