introducing a non-uniform heat source

[bonbonblond]

In branch 77, we introduced a heat source that is uniform in our column. We want it to be more complex, thus not uniform.

[flipoyo]

Before doing that, please close the other issues linear system, introduce heat source, with proper pull requests

[flipoyo]

Another step before programming non uniform heat source is to elaborate an assessment of the new software performances, with and without q for the inversion.

[bonbonblond]

With the hypothesis that the lateral flow is moving from the column to the exterior.