[nemo-qml-plugin-contacts] Add export mode to vcardconverter

Only exports local contacts.
[nemo-qml-plugin-contacts] Add option to export aggregate data
Revert "[nemo-qml-plugin-contacts] Add option to export aggregate data"

This reverts commit 38c35de42da055067f2c8af3b9b2775c53959338.

Export of aggregate data is not possible, since the vcardconverter tool
will be a privileged application, and non-local data in the privileged
contacts database should not be exported.
Merge pull request #51 from matthewvogt/export

[nemo-qml-plugin-contacts] Add export mode to vcardconverter