[contactsd] Handle deletions from export DB without imports

When import-changes-from-exported-database is not configured, changes
made to a contact in the privileged database cannot be applied
directly to the export DB if the updated contact has been removed.
In this situation, the changes need to be converted to a re-addition
of the modified contact in its new state.
Merge pull request #69 from matthewvogt/handle-removal

[contactsd] Handle deletions from export DB without imports