I.e., remove the shell invocation and with it the need to set the shebang.
Surprisingly this required some build-system modifications particularly
for cmake in order to correctly set the environment.
It is split into
- /libgnucash (for the non-gui bits)
- /gnucash (for the gui)
- /common (misc source files used by both)
- /bindings (currently only holds python bindings)
This is the first step in restructuring the code. It will need much
more fine tuning later on.
