[filename, backupFile] = pwSaveModel(model, filename, proposedFilename, openInEditor,
Saves a model as a valid PottersWheel model definition file.
model If empty (), the currently selected model is saved.
If a number, the corresponding model in the repository
list is saved.
Else, a model struct is expected.
filename If filename is not given, a file saving dialog opens.
If the file already exists, PW tries to create a backup file
if config.general.doBackup == true.
The filename without path and extension will be used as the new model ID.
The complete filename will be returned.
backupFile Name of the backupped old model file (if any).
includeComments Help comments can be included into the model comprising a short
description and examples for all essential model sections.
openInEditor true by default