This is achieved by moving ClauseHeader::{AbstractOperation,Accessor,
Method} to Function.h itself and storing them in FunctionDeclaration.
This commit also introduces QualifiedName class that is used to store
function's name split by '.' (just like it appear in the spec).
This SpecParser.cpp had an ever increasing number of lines and contained
an implementation of 8 different classes. So I figured out it's about
the time to split it.
No behavior change.
