RvtkStatismo now supports im- and export of ModelInfo

After struggeling with the documentation of statismo, I found out that things had changed: Instead of

KeyValueList DataInfo = model->GetModelInfo().GetDataInfo() 

I had to do

BuilderInfoList binfo = model->GetModelInfo().GetBuilderInfoList();
if (binfo.size() > 0) { 
   KeyValueList DataInfo = binfo[0].GetDataInfo();
   ...

For implementing the modelinfo into pPCA, I created a new private S4 class called modelinfo that stores the lists datainfo and paraminfo. Both contain two-valued character vectors - similar as in statismo. These contain the first entry of the BuilderInfoList:

BuilderInfoList binfo = model->GetModelInfo().GetBuilderInfoList();
KeyValueList DataInfo = binfo[0].GetDataInfo();
KeyValueList BuildInfo = binfo[0].GetParameterInfo();