Generalize exceptions

[fcollot]

One of the major architectural changes I would like to make to MUSIC is to fix the current error handling mechanism which isn't very well standardised and has a lot of code cloned here and there. This is important because currently when the program fails, depending on what failed, it sometimes crashes, sometimes does nothing, sometimes gives a warning that is not easily visible etc. The overall user experience is frustrating.

Currently the code is split up between parts that use error codes and parts that use exceptions. It doesn't help that DTK uses error codes, ITK uses exceptions and VTK doesn't use either but uses events (so you have to add an observer for the error).

There is a lot of debate about which one is better, but I personally prefer exceptions and after having transitioned from error codes to exceptions in the pipeline system there is no doubt for me that they are much better suited to the architecture of MUSIC.

[fcollot]

(There is a large part of the code that doesn't do anything when there is an error, and simply returns from the function. This is equivalent to ignoring errors altogether and makes it impossible to debug properly).

[fcollot]

As mentioned in https://github.com/Inria-Asclepios/music-clinical-pipelines/pull/20 I'm working on the issue of error handling.