#1524 Roll back slightly: the use of SFINAE was resulting in not very clear compilation messages; not it's done with a static_assert which gives a much better hint of what doesn't work as intended.

#1525 I have taken VectorIO test as an example of how to avoid to use a Model for a test - and therefore avoiding the fields related to TimeManager. It is to be seen as a proof of concept: there is a bit of work to make this more palatable to write (but in the end we should get more agreeable tests with no longer loads of useless boilerplate parameters in the input data file.

For XCode users: a Model library has been reintroduced as there is now a compiled file inside (no change for CMake build: the Model library was already existing - but was empty so far).