Move constants to separate file

[jbienkowski311]

Description

Moves constants to separate file. Now one can import only constants if needed.

Motivation and Context

Implements #205

How Has This Been Tested?

npm test - all green

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I have read the code of conduct.
• I have read the contributing guide.
• I have updated the documentation accordingly (if applicable).