Layered standard: SSV parameter files in an FMU

[chrbertsch]

(From a discussion a the FMI Design meeting with @pmai and @klausschuch)
The SSP Standard (https://ssp-standard.org/publications/SSP101/SystemStructureAndParameterization101.pdf) defines System Structure Parameter Values (SSV) xml files. In order to use them currently for an FMU, one has to include the FMU in an SSP file and ship this SSP file.
However, if one only the paramater set feature of SSP is needed, a more lightweight solution would be a layered standard, that defines to include SSV files (defined by the SSP Standard) in a /extra/LS-PARAM/ folder.

Use case:

• Provision of several parameter sets for the FMU, that can be selected by the user in tools that support this Layered standard. The SSV files could be created by the exporting tool, or added later (by separate tools or manually by the user)