Make exported metamodel integration easier

[gblondet117]

Exporting a metamodel with, for instance, export_model() generates a .mo files containing a function, link to a binary file.

It is a bit difficult to integrate this properly to a modelica master model. User must :

1. create a directory to pack the .mo and the libcwrapper.a file, since they are strongly dependant, and move them to the modelica master model.
2. change the metamodel.mo file to add "Within ........ ;" line in the header , AND update the LibraryDirectory path.
3. change the package.mo and package_order.mo of the existing target modelica package;
4. Create a package.mo and package_order.mo inside the directory of the metamodel.
   It may be automated, mostly, by otfmi.