IIR EQ base class

This introduces a common base class for all fidlib based Filters.
It makes use of templates to be generic as possible, without introducing CPU overhead. 
It was a design goal to remove them as member variables. Currently I do not need them. IMHO this way the compiler is able to optimize most. Maybe a const member vanishes as well, but it is better to not have it at all.   

Please explain why you think the code is more clear with it.