updated toy_example including the trench "Ettlinger Linie"

Smaller maintenance updates with quite a few bug fixes.

# Conflicts:
#	src/IFOS2D.c

I removed the zero phase option from the code, due to complications depending on the source signal and the time window. However, from a technically point of view it was implemented right.

Position 7 in workflow is now F_HIGH_PASS.
All other parameters have been shifted.

The model, which is used in the step length estimation is outputted if VERBOSE is set to 1.

Both L2-misfits are now normalized at each iteration. Therefore, both objective functions should be weighted equally.

The sinus3 source wavelet was shifted in the wrong direction.

Added references to D. Koehn's dissertation. Large parts of the theory are extracted from his dissertation.

Position 7 in workflow is now F_HIGH_PASS.
All other parameters have been shifted.

The vector FL was allocated before the value L was exchanged.

This fix will reset the conjugate gradient history each time a frequency or workflow stage is switched.
If such a stage is switched we will have a "new" objective function, thus, it makes no sense to use the old gradients for speeding up the convergence.
This bug was the reason why the objective function could not be reduced for 2-3 iterations after a new frequency stage was appplied.