Port to Ogre 1.9.0

I've tried to build Vertigo against OGRE 1.9.0 on Mageia 5, and after some tweaking to get the dependencies installed (ParticleUniverse and OgreOggSound), I hit errors relative to Ogre, namely (excerpt):

```
g++ `pkg-config --cflags OGRE OGRE-Overlay OIS bullet` -Iinclude -Imodules/include -Imodules/include/ogre -Imodules/include/ogre-procedural -Imodules/include/btogre -Imodules/include/tinyxml -Imodules/include/tinyxmlresource -I/usr/include/OGRE/Plugins/ParticleUniverse -I/usr/local/include/OgreOggSound -O2 -c src/Tunnel.cpp -o src/Tunnel.o
In file included from include/UIEngine.h:35:0,
from include/Level.h:31,
from src/Tunnel.cpp:24:
modules/include/ogre/OgreSdkTrays.h: In static member function 'static void OgreBites::Widget::nukeOverlayElement(Ogre::OverlayElement*)':
modules/include/ogre/OgreSdkTrays.h:139:5: error: incomplete type 'Ogre::OverlayManager' used in nested name specifier
Ogre::OverlayManager::getSingleton().destroyOverlayElement(element);
^
modules/include/ogre/OgreSdkTrays.h: In static member function 'static bool OgreBites::Widget::isCursorOver(Ogre::OverlayElement*, const Ogre::Vector2&, Ogre::Real)':
modules/include/ogre/OgreSdkTrays.h:148:31: error: incomplete type 'Ogre::OverlayManager' used in nested name specifier
Ogre::OverlayManager& om = Ogre::OverlayManager::getSingleton();
^
modules/include/ogre/OgreSdkTrays.h:149:59: error: invalid use of incomplete type 'class Ogre::OverlayManager'
Ogre::Real l = element->_getDerivedLeft() * om.getViewportWidth();
^
In file included from /usr/include/OGRE/Overlay/OgreOverlayContainer.h:32:0,
from /usr/include/OGRE/Plugins/ParticleUniverse/ParticleUniverseSystemManager.h:56,
from include/Probe.h:33,
from include/Tunnel.h:27,
from src/Tunnel.cpp:22:
/usr/include/OGRE/Overlay/OgreOverlayPrerequisites.h:43:11: error: forward declaration of 'class Ogre::OverlayManager'
class OverlayManager;
^
```

It would be nice to get the code base updated for recent libs, so that the game can still be built in recent environments (and maybe attract new contributors, or at least distro packagers?).