classLoader should handle multiple versions of the same library

[Martin Sjölund]

17.7.3
Mapping of Versions to File System
A top-level class, IDENT, with version VERSION-NUMBER can be stored in one of the following ways in a
directory given in the MODELICAPATH:
The file IDENT ".mo" [Example: Modelica.mo]
The file IDENT " " VERSION-NUMBER ".mo" [Example: Modelica 2.1.mo]
The directory IDENT [Example: Modelica]
202 Modelica Language Specification 3.2
The directory IDENT " " VERSION-NUMBER [Example: Modelica 2.1]

Solve by for example doing strncmp of libraries in the path... Pick the latest version (default to 3.1 for Modelica), etc.
Then we should augment the loadModel() command to also accept calling it by loadModel(Modelica,"3.2 beta3")

After that, we can change the directory structure for our libraries (again).

[Martin Sjölund]

I can probably work on this during the design meeting. Would mean we need less env.vars for testing