Revert "Added special case in paramDefine when creating a parametric param"

This reverts commit 8a3638e1d32cb29b0f6e20f200a13f1cdd3e3a4a.
Revert "Moved the parametric specific prop setting to ofxhParametricParam.cpp in the constructor of the ParametricDescriptor, as we need them at the time of the constructor to be able to set a hook on some properties."

This reverts commit 7386690c1ede148eb246d8d42c7961a218d53ca3.

The Descriptor class is generic and shall be used for all parameters.
Parameter-specific handling and data storage go to the instance.
The OpenFX doc mentions that the default control point should be stored
in the descriptor:
http://openfx.sourceforge.net/Documentation/1.3/ofxProgrammingReference.
html#id479272
« To set the default value of a parametric parameter to anything but
the identity, you use the control point setting functions in the new
suite to set up a curve on the descriptor returned by
OfxParameterSuiteV1::paramDefine. Any instances later created, will
have that curve as a default. »

This can easily be implemented using a private Double X 3N property on
the descriptor (let’s call it OfxParamPropControlPoints, and define it
in ofxhParametricParam.h, since it’s host-specific), where we store
(curveIndex, key, value) triplets. Only the control points need to be
stored. The descriptor does not need to handle the curve stuff : no
getValue, no tangents/derivatives, etc. It’s just a place to store
default values.

-> @MrKepzie