Add Boundary Conditions in output of feelpp_toolboxes exec

[Trophime]

It will be helpful to have the list of boundary conditions printed in the output of feelpp_toolboxes exec
just like we have the materials.

This feature seems to have disappeared from latest version.

[vincentchabannes]

Boundary conditions are not printed because the output system has changed. It requires adding some codes but I planned to review fully the base class of boundary conditions (and therefore not to do the work twice). It will be available as soon as possible...