Add interfaces to allow integration of PyMAPDL and PySystemCoupling about pymapdl HOT 1 OPEN

Hi, this seems like a good idea, however I have some comments.

• Any integration should be optional and it should be general. Ideally, a framework for installing PyMAPDL "extensions" is desirable. I must do more research about this yet.
• The mentioned "duck typing" should be seen also as "composing" the classes. More on this later.
• Regarding wrapping mapdl.sf and such commands. This might be a good idea, in some cases, but I think it is more reasonable to have some mapdl methods which can extract the information you need (getter) instead of wrapping the command which set it (setter).

Regarding "composing" the classes.

I think PyMAPDL should offer a way to extended the current mapdl class by class composition.

I think we should allow to install packages as ansys-mapdl-core-%extension%. This packages should have a function,
that has the mapdl class as input, and prepare the module as the extension writer intends to.
To load it, PyMAPDL will automatically checks for packages with such definition, and load dynamically a method with the intended name.
I shall come up with sort of pseudo code

from pymapdl.