MT#5879 Allow to skip empty invoices generation with option no_empty.

(cherry picked from commit ae8515d6024df6ac01140a1fd15f209fbcdab33c)
MT#5879 Remove Country processing warning.

(cherry picked from commit 9d80cba5fd51314bd4909505fc09ce05aa232080)
MT#5879 Fix billing_mapping logic, use the latest one as actual.

(cherry picked from commit b90be26a2e6fad716c131640db2fd03c040084af)
MT#5879 Fix memory issue

Don't save or fetch data for all generated/sent invoices.
Fetch data one-by-one.