* modules/gui/wxwindows/*: don't forget to delete the timer.
   Use wxApp::OnExit() to cleanup the dialogs provider.
   Added a "Miscellaneous" section to the menu. Added a "Switch interface" and "Add interface" entries to this menu.
* modules/gui/skins/src/*: dialog providers have object types of VLC_OBJECT_DIALOGS.
   Don't forget to attach/detach the dialogs provider to its parent intf.
   Work around a bug in imlib2 when we close the plugin.
* src/misc/objects.c, include/vlc_objects.h: added VLC_OBJECT_DIALOGS for dialogs providers.
* src/interface/interface.c, include/vlc_interface.h: added 2 object variables to switch/add interfaces on the fly (intf-switch and intf-add).