Refactor VRPN Server/Client API + VTKViewer window management

VRPN: Allows for the following workflow :

1. Create a VRPNDeviceClient by specifying its URL (name@ipadress) and its type (see DeviceType class). The subclass VRPNForceDevice is setting the style to PHANTOM_OMNI by default for now.
2. Create a VRPNDeviceServer
3. Call VRPNDeviceServer::addDeviceClient() to add the client created on step 1). This will analyse the IP, name, and type of the device client to instantiate a VRPN device connection. The added devices are then stored in three std:map so the mainloop() can be called during the execution.

Updated their use in FEMSimulator and LaparoscopicCamera examples.

VTKViewer: implementing setVtkRenderWindow

• This calls VTKRenderer::setRenderWindow. Needed to use a vtkRenderWindow from another instance (example : for a QT application, use QVTKWidget renderwindow)
• Rename VTKViewer::getRenderWindow to getVtkRenderWindow
• Use internal functions in getVtkCamera and getVtkRenderer