Complex-Math: Handle Operations with Scalars

First feature from @BeyondEspresso 's pull #597.

Updated the complex-math library in the radiation-plugin to handle all basic calculations (+,-,*,/) and assignment from scalars.
I am a little bit confused that this compiles. Normaly `Complex_T`is no type without the template definition.

IMO it should be: 
```C++
typedef Complex<Type> ComplexType;

HDINLINE friend ComplexType operator+(const ComplexType& lhs, const ComplexType& rhs)
...
```

If it is right C++ Syntax than I am not sure if it is type save (e.g. ```Complex_T<double> != Complex_T<float>``` must be true).