feat: add "Hexshade Green" dark green theme

[simonantonio]

All Submissions:

• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

New Theme Submissions:

Have you included all the required elements?

1. Have you included all the required elements in your theme?
2. Are images in the correct resolution?
3. Have you updated the readme.md to include reference to your creation (please add to end of the list)?

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Adds a simple dark green theme with hex shape background

[pfeerick]

Thank you for your contribution... it looks nice! :)