feat(seasonal): Implement snowball

Minor refactoring of special spell purchasing, and turns snowball into Gold- instead of Gem-purchasable.
feat(NYE): Image resources
WIP(NYE): New Year's Cards
feat(NYE): New Year's cards
fix(NYE): I18N shop text
fix(NYE): Card to self exploit
fix(NYE): t undefined
fix(NYE): I18N for random text
feat(NYE): Silly Party Hat
Merge pull request #425 from SabreCat/nye

New Year's event features