Add missing payment info template for PDF generation

[cmuench]

Description

The adminhtml area contains a default template for all payment methods
which comes without an own payment info template.
If you generate a PDF by clicking the "Print PDF" button i.e. the
invoice generation you will see correct payment informations.
If you generate a PDF in frontend you have an empty payment info because
of the missing template. The info block is returning an empty string
instead.

Manual testing scenarios

1. Create an order with "banktransfer" payment.
2. Add an order and attach a PDF invoice (i.e. with an own module)
3. Download the invoice.
4. Payment info is empty

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[miguelbalparda]

Thank you for your contribution @cmuench! When you say

If you generate a PDF in frontend

does that mean programatically?

[vrann]

@cmuench thank you, merged!

[magento-team]

@cmuench thank you for your contribution to Magento 2 project

[cmuench]

@miguelbalparda There is no PDF download link available in the frontend area. If we will add a download link in the future to Magento frontend we would have an issue without this changes.
We had already an issue in one of our projects, because we create a PDF file programmatically via a cronjob by using store emulation.