Avatar measurement isn't accurate enough

[xyonico]

Make the measurement more accurate and also include hotkeys for manually scaling the avatar.

[Ibodan]

My branched release with body scan is just for curious. I am sure that scaling up/down manually with keys is better for ordinary people. I will start to work on it at least on next week, now I'm away from development environment.

If you prefer scaling avatars with their arm length, you can merge that thing into main branch by any ways you would like to such as ordering me to make a pull request or re-implement by yourself.