[BUGFIX] Wrong usage of use statement

Resolves errors like "The use statement
with non-compound name 'Client' has no effect"
Merge pull request #169 from opendo/master

[BUGFIX] Wrong usage of use statement
Fixed bug where the incorrect credit balance was updated
Added Spanish translation
Added tax percent to PDF
fix #170 - Live PDF not rendered when using logo
fix #171 - Quote to invoice should change the Prefix and the number
Improved the spanish translation

It still need some more improvement, im working on it.
Added Factura de Venta

To comply to Colombias law invoice should translate to "Factura de Venta"
Merge pull request #175 from wanchopeblanco/master

Improved spanish translation
Added payment gateway help/sign-up links
Merge branch 'master' of github.com:hillelcoren/invoice-ninja
fix #168 - Allow :MONTH, :QUARTER or :YEAR for products even when the invoice is not recurring
Improved the spanish translation

Some more improvements for the spanish translation.
Added support for a demo account
fix #174 - Tax rate error in live PDF
Merge pull request #179 from wanchopeblanco/master

Improved the spanish translation
Enabled using date variables for non-recurring invoices
Merge branch 'master' of github.com:hillelcoren/invoice-ninja
Enabled using date variables for non-recurring invoices