Extend support for keyword args and placeholders

[GuntherRademacher]

The support for calling user-defined functions needs to be extended by

• handling keyword arguments,
• establishing the correct order of parameters of partially evaluated functions. This may deviate from the order in the target function when placeholders are used for keyword arguments.

This change

• adds a call to prepareArgs to Functions.dynamic, in order to integrate keyword arguments into the positional argument list.
• calculates a permutation of placeholder ordinals, mapping the i-th placeholder in the integrated positional argument list (for the target function) to its position in the parameter list of the partially applied function,
• propagates the type to the parameter variable, in order to enable item coercion,
• disallows keyword arguments in dynamic function calls during parsing.

The corresponding QT4 test cases are

• FunctionCall-414
• FunctionCall-415
• FunctionCall-416
• FunctionCall-417