Hotfix: Inspect all of codes

[seoulsky-field]

What

• Inspect and revise all of train, utils, inference codes.
  

Why

There are some codes set default settings such as num_classes = 5. Before experiments and adding more functions, or hyper-parameter tunings. More, if the file which didn't apply pre-commit exists, it would be applied in this issue. In addition, if it's more reasonable to use name "utils" rather than "custom_utils", it can be changed in this issue.

Notes: This issue doesn't have relation between working well currently. The purpose of this issue is "checking the codes", not "working well about all of options".

How

• [x] Inspect & Revise trainer
• [x] Inspect & Revise inference
• [x] Inspect & Revise custom_utils

[seoulsky-field]

This issue has completed. Also, this branch is merged to the branch of issue #80 .