For each subclass, getting rid of GNC_SQL_OBJECT_BACKEND_VERSION which
was a bit misguided.
Also remove the bogus test the skipped loading a table if its version
didn't match GNC_SQL_OBJECT_BACKEND_VERSION which was even more misguided.
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.
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.
