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).
In a nutshell, when we understand that the expression is a function
call (this happens at '(' after an expression), stop parsing expression
and start parsing function arguments. This makes
`FunctionCallCanonicalizationPass` and the workaround for zero argument
function calls obsolete.
