Different skin / theme for blockly

This is a shallow point, but it might be good to replace the default blockly theme with something that looks different.

Here's why: students will immediately recognize the blockly look and feel, and associate it with "Hour of Code" activities they've done using https://code.org/learn We don't really want them to compare this to Hour of Code activities. Hour of Code activities are heavily branded with commercial partnerships involving favorite video games and TV shows, and are designed to require only a minimum effort to get a slightly customized (but mostly pre-made) result. The goal should be for this to feel like something different, where the kids are creating something entirely their own. But when the UI looks the same, it will make many kids think it's just the same tool.

Not a high priority, though.

En el issue no se identifica ningún archivo, prueba ni punto de entrada. Empieza por localizar la Blockly UI y su integración actual de themes, y determina después cómo se configuran los themes. Se considera terminado cuando la interfaz tiene un theme visual distintivo en lugar del aspecto predeterminado de Blockly.

Escrito por el modelo de indexación a partir del texto del issue.