MT#8371 Make customer queries up to 10 times faster.

More possibilities in billing_mapping history separation.
MT#8371 Fix for optimized query build

Remove double join for billing_mappings
MT#8371 Additional changes for actual billing_mapping optimisation.

All billing_mappings for contract are linked now through
billing_mapping_actual view. Datatables configurations changed accordingly.
MT#8371 Remove duplicate joins contracts_rs with billing_mapping.
MT#5879 Fix for contacts without contract.
MT#5879 Inital config and cron files for invoice generation script
MT#5879 Save own parsing of config.
MT#5879 Fix manual page and fix using centralised config in generator