Improved prop_thumper

[Wikot235]

Mappers can now customize color of the dust that is emitted by prop_thumper. If a map doesn't have a defined dust color, dust color value is NULL, that makes it 0 0 0, it would create a black dust, to circumvent this, there is an if statement that detects if dust color value is 0 0 0, if yes, it replaces 0 0 0 with the original color. If a mapper want's the dust to have a black color, they can set the color value to 1 1 1, as it looks the same as 0 0 0.

I have also added new spawn flags:

-Start disabled
-No dust
-No shake

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