Add support for device classes

Changes

• Small code cleanup (#18) @danieldotnl
• Support for device_class
• Significant code cleanup (moved constants and schemas to own file)

📦 Dependencies

• Bump pip from 21.1.1 to 21.1.2 in /.github/workflows (#21) @dependabot
• Bump pre-commit from 2.12.1 to 2.13.0 in /.github/workflows (#22) @dependabot
• Bump black from 21.5b0 to 21.5b1 in /.github/workflows (#17) @dependabot
• Bump flake8 from 3.9.1 to 3.9.2 in /.github/workflows (#16) @dependabot
• Bump black from 21.4b2 to 21.5b0 in /.github/workflows (#15) @dependabot