Billing Based On Usage

[flangefrog]

I would like to see a feature that allowed a module to give the usage of an service such as bandwidth or VOIP minutes. Blesta would find the usage at the time of creating the invoice via the modules getUsage function or something similar. There would also be an option to allow the client to view there usage. This would probably help increase adoption of Blesta for small ISPs and Telcos.