The function for calculating the self-energy was renamed and split into
smaller subroutines. This makes future implementations of similar
functions easier.
A bug when calling the abinitiodga executable was also fixed.

This allows to run multiple Jackknives at the same time.

Also print the execution time

This reverts commit b6e8b134.

Also print a lot of diagnostic messages to find out why the output
of symmetrize.py stays the same all the time.

A test is added where the original x_i are transformed to y_i and then
basic statistics are done with those y_i to get the sample mean,
variance and standard deviation of the y_i.