This version is available for all supported platforms and distros
(CentOS can have a version via EPEL, which is required anyway)
Advantages:
- one cmake version for all platforms
- we can drop all conditions based on cmake version
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.