Improve UX with spatial tracking device and reference mode selection

[vhosouza]

From the user perspective, it is not intuitive and efficient to have a list of spatial trackers to select from. Usually, the users have only one device and that's the one they will be using for all experiments. This is similar to selecting a language, once you pick the UI language, you won't be changing it every time.

I suggest we replace the dropdown menu for selecting the spatial tracker by a push button named Connect, which would connect to a default tracking device selected either in the first run of invesalius or the first time the user click the button. The user would have the possibility to change the default tracker by going to the upper menu Options > Preferences > Neuronavigation. This tab does not exist, so needs to be created. The deafult values would be writen in the user-specific .config file.

We could also move there the Reference mode dropdown menu (Dynamic or static), as it follows the same user approach than the tracking the device.