supported by sqlite, so choice is hidden

abstract because this break compatibility with a lot of external module
and generate FATAL errors after migration. Because PHP is not yet able
to manage try catch on FATAL error, we can't catch such error. Using
bstract on constructor is so postponed.

Created abstract functions DolibarrModules::__construct, DolibarrModules::init and DolibarrModules::remove

Added missing fields
Removed unused variables
Documented methods parameters
Checked return points

Best practice