Fix mod version compatibility checking for major version differences

[Fank]

Summary

This PR fixes issue #517 where the auto mod updater was downloading incorrect mod versions after updating to Space Age (Factorio 2.0). The mod updater would download 1.x versions of mods instead of the compatible 2.x versions.

Problem

The version checking logic in check_game_version() was incorrectly implemented:

• It was comparing versions in the wrong order (checking if mod version >= game version)
• It wasn't properly handling major version differences for backward compatibility

Solution

• Fixed check_game_version() to properly check if the current game version satisfies the mod's minimum required version
• Game versions can now run mods designed for older major versions (backward compatibility)
• Game versions correctly reject mods requiring newer versions than currently installed
• Fixed variable references in check_dependency_version() that were using $FACTORIO_VERSION instead of $mod_version
• Added clarifying comments about the version checking behavior

Testing

The fix has been tested with various version combinations:

• ✅ Factorio 2.0 accepts mods requiring 2.0
• ✅ Factorio 2.0 accepts mods requiring 1.1 (backward compatibility)
• ✅ Factorio 1.1 rejects mods requiring 2.0
• ✅ Version comparison within same major version works correctly

Related Issues

This also addresses issue #468 by ensuring mods requiring newer Factorio versions than currently installed are properly skipped.

Fixes #517
Fixes #468