:open_umbrella: setup guidelines for contributing

[scarf005]

Summary

• add CONTRIBUTING.md
  • move install guides to CONTRIBUTING.md
  • add commit style guide
• add LOCALIZATION.md
• setup code style
• fix obsolete gradle task description
• properly address license #103
• add semver guideline #109
• label new PRs
• add description about steamworks error code
• embed changelog generation script inside repo #155
• guide on how to enable basemod terminal