Fix #802; structure.xml should contain full messages

Errors in the generated structure.xml did not contain a complete
error message, instead the error code was registered. To fix this
issue a new interface for writers was introduced to declare that
they should support translation of items and the XML Writer
should use that to translate the code into a message.
[#787]: Trim package name

When setting the package name it should be trimmed to that no awkward packages
are created that end in spaces.
Add exception to vagrant file so that NFS is only used with Linux and MacOSX