Add Currency and ExchangeRate models
Some fixes in filters
Merge pull request #80 from 10Pines/fixes_in_filters

Fixes in filters
Revert "Add Currency and ExchangeRate models"

This reverts commit 54a4a327cf58436efb23942de905448109e2902a.
Add amount in original currency to Comprobante
Add validations to Comprobante and specs
Render original amount fields on comprobante show
Improve filters for original amount fields
Add automatic calculation of net amount from amount in original currency
Simplify binding of event on multiple fields
Add currencies administration
Fix label_for
Add unique validation to currencies by name
Fix redirect after update or create a currency
Change order of fields