Merge branch 'improve-vrpn-device-api' into 'master'

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`

See merge request !72