updated toy_example including the trench "Ettlinger Linie"

Implemented an offset based tracekill for STF.
Makefile in par folder has now two new targets:
1. make install, do an install from precompiled files
2. make reinstall, do a clean install

(1.)
Renamed function err() to declare_error().
This was a problem, as many standard libraries also has functions err().

(2)
I fixed a lot of compiler warnings like unused variables and uninitialised variables. However, here is a lot of work to do.

Changed naming convention of individual spatial tapers for gradients, updated to usage with WORKFLOW

Update: Merge test

For the exchange of the wavefields a wrapping layer of FDORDER/2 is needed.
Nevertheless a wrapping layer of FDORDER/2 +1 was implemented because of undetected errors in the exchange functions.