Utils/gitlab

The new machine is better. It is now possible to compile the code
using the '-j 4' flag

Feature/explicit acoustic solver rewrite

See merge request !79

Algorithm directory is now emptied (in this branch at least)

The idea is that if a source file is removed, its associated .gcno and
.gcda files remained, leading to a crash of lcov (non finding expected
sources)

This allows to write the time loop directly in the pgs file.