fmiModelDescription could use version attribute

[beutlich]

The fmiModelDescription node of the modelDescription.xml could set the version attribute as separate meta data and not merged with the generationTool. Intead of

<fmiModelDescription
  fmiVersion="3.0"
  modelName="BouncingBall"
  description="This model calculates the trajectory..."
  generationTool="Reference FMUs (development build)"
  instantiationToken="{8c4e810f-3df3-4a00-8276-176fa3c9f003}">

have

<fmiModelDescription
  fmiVersion="3.0"
  modelName="BouncingBall"
  description="This model calculates the trajectory..."
  generationTool="Reference FMUs"
  version="development build"
  instantiationToken="{8c4e810f-3df3-4a00-8276-176fa3c9f003}">

Thanks.