C0103 fixes 3, dht, k_bucket and routing_table

This PR is dependent on #1108.
Do you mind renaming that to `touch_kbucket`? There is an actual class named `KBucket` and I would like the name to evoke is as much as possible.

There are a couple of places inside `constants.py` and `dht.py` where a `KBucket` is mentioned as `k-bucket`. Please rename them using `KBucket`.