Combine packages on import.

[ditmarvisser]

As described in #142 I am not able to import my complete language package at the moment. For now I have uploaded 1/3 of the complete package to Vocascan. I would like to be able to upload the rest of the package, but have the new content be added to the current package instead of creating a new package. I do not want to have to upload 72 groups individually.

Maybe when importing a package that has the same name as an already existing package there can be a warning with a choice to add the new content to the existing package, or create a new one with the same name.

[luwol03]

Im thinking of having the possibility to have the group type file as an array type, so a > vocascan/group file can contain multiple groups which can be imported at once into a package.