Main math operators and delete button

NEW:

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Finally: you can use this calculator like a real calculator. I've added the main mathematical operators, so you can make use of the fancy calculator.

Additionally, I've been created a delete button, thus you're now able to delete the whole calculation if you have mistyped.

I welcome any criticism, feedback or suggestions, so feel free to write me.

And now enjoy yourself with the breathtaking calculator.

And thanks for the partial help @Fornball.