Fixed warnings "unused variable" in GeoMapper.
Fixed warning related to the sequence of attributes in initializer list.
Fixed warning unused variable in ElementExtraction::searchByBoundingBox().
Fixed warning "comparison between signed and unsigned" in GeoTreeModel::setNameForItem().
Fixing unused parameter in MeshElementRemovalDialog::on_meshNameComboBox_currentIndexChanged().

The parameter is necessary due to a fixed signature in Qt signal concept.
Prevent compiler error in case Eigen is not available.
Merge pull request #281 from TomFischer/StNicholasWarningsFixDay

St nicholas warnings fix day