The change is only relevant to development as all the call to python scripts is done
calling C++ os::python that invoques the appropriate python version.
The change is two fold, on one hand remove all the uses of /usr/bin/env for python.
On the other hand rename all the calls to python from python to python3 making it explicit
and being compliant with PEP 394 -- The "python" Command on Unix-Like Systems:
https://www.python.org/dev/peps/pep-0394/
Remove the sheebang from src/graphics/GraphicsConverter.cpp because it is not necessary.
Some small whitespace changes.
Some macros defined by wasysym.sty work only in text mode: They either
produce an error in math mode, or wrong output. These symbols are now marked
as text symbols, so that no \ensuremath is created for LaTeX export if they
appear inside \text{}, and the correct images are created.
development/tools/generate_symbols_images.py now checks for each symbol in
lib/symbols whether its image is listed in lib/Makefile.am and whether it has
a toolbar entry in lib/ui/stdtoolbars.inc.
