[nemo-qml-plugins] Populate NameGroupModel correctly if it is loaded after contacts cache.

Previously if it was loaded after all contacts were loaded by
SeasideCache, it would not be populated.

Also fixed NameGroupModel to emit countChanged().
Merge pull request #145 from blammit/fix-name-group-updates

[nemo-qml-plugins] Populate NameGroupModel correctly if it is loaded aft...