Gravity Platformer Fix (#1965)

* Create gravity-platformer.js

* Added coin mechanics and new levels

* Added new levels and started work on the end screen

* Added the start and end screen, refactored some code and added comments

* Fixing metadata

* Update gravity-platformer.js

* Update gravity-platformer.js

* Fixing metadata

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Co-authored-by: graham <[email protected]>

Author: notrewd