fix two QT warnings in explorer widget

Warning: QWidget::setLayout: Attempting to set QLayout "" on
OpenGeoExplorer "", which already has a layout

Warning: QMainWindow::saveState(): 'objectName' not set for
QDockWidget 0x3a76f60 'OpenGeo explorer;
Merge pull request #61 from ischneider/fix-warnings

fix two QT warnings in explorer widget