Support for ExpandableVariables

[maforget]

This fixes #344, there are no support to change the path in the GUI. I just change the path in the config.json directly. Also since the API uses the Game for some Variables and some of the methods don't supply it, I just new Game() instead in that case. So it will work with {PlayniteDir}, but might not always work with other Variables that require the Game object.

Did this for personal use, feel free to use it or modify it if required.

I have verified that:

• [x] These changes work, by building the extension and testing.
• [x] That the changes comply with the rules indicated in the repository.
• [x] Pull request is targeting master branch.

[darklinkpower]

Please also make the paths text field editable from the extension settings page

[maforget]

Done