ThingML split of platform independent and platform specific

[sdalgard]

The project architecture in the ThingML training tutorial put the "top level configuration" into the platform specific files.
This results in duplication of platform independent configuration for all the platforms.

We should have a project architecture where platform specific files are like libraries (make and dont touch). The configuration section should be split into at least two sections.
The platform independent configuration section should be the top where the code generation is started for N targets.