[nemo-qml-plugin-contacts] Do not change filter type for required property

Although the required property casues the results to be filtered, we
should only switch between FilterNone and FilterAll modes due to changes
to the filter pattern.
Fix test data
[nemo-qml-plugin-contacts] contactcache now exports internal ID lists
Remove obsolete function declaration
Merge pull request #55 from matthewvogt/jb9408

Do not change effective filter type for requiredProperty changes