Improvements to the CSV generator

In Abiquo 6.1.2, the following improvements were made to the CSV generator.

• Add an option to enable/disable headers for the CSV

• Change usage_init_date and usage_end_date to be date parameters

• Add group by usage_name for onpremise option to separate different extra charge costs

To use the CSV generator for a reseller, first add a RESELLER_CODE enterprise property to your reseller enterprise. Abiquo recommends that you set the value to a short code (e.g. 3 letters) to easily identify the reseller in cost usage reports.