feat: Inject package.json version into the app

[bastienwirtz]

Description

This provides

• An access to app version in the javascript code as a global variable
• Add a VERSION text file to the build, containing the current version as a simple string.

Fixes #745

Type of change

• 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)
• Refactoring

Checklist:

• I've read & comply with the contributing guidelines
• I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• I have made corresponding changes to the documentation (README.md).
• I've checked my modifications for any breaking changes, especially in the config.yml file