gst-element-ui-prop-view: cleaned up the file open button and do not rely on gtk_dialog_run()
gst-element-ui-prop-view: cleaned up the file open button and do not rely on gtk_dialog_run()

 * fixed URI handling: there are actually specialized file chooser methods...
 * no longer use gtk_dialog_run() for selecting files with the GtkFileChooser.
   gtk_dialog_run() does not work when embedding the glib event loop into libev for instance
   since we cannot call into the glib event loop.
 * The implementation now should work as before but interfer less with the embedding application.

metratec/gst-editor,metratec/gst-editor,metratec/gst-editor,metratec/gst-editor