VERSION variable in root

[jdsika]

Currently every package has its own version number. We decided to release on GitHub with a protected tag v* and use the same version in all NPM packages to avoid confusion and enforce consistency.

• add the version number to a VERSION file in the root directory and use a variable in all places where the version is used

[jdsika]

This tool seems to be a good way on how to solve it: https://github.com/jscutlery/semver