This will avoid a ninja-build from picking up a config.h generated by the autotools build
(in the root build directory). Picking up the wrong config.h may lead to all kinds of
subtle issues if the autotools run was done with different options than the cmake run.
gtk-mac-bundler can't access the executable's rpath list so it can't
follow dependencies if they're not in $install_dir/lib from @rpath.
Autotools always sets absolute path install names so this should have no
adverse affects on other Mac builds.
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.