Changeset 8657

WordCamp: Add CampTix Invoices plugin to codebase

This adds CampTix Invoices directly to the WordCamp codebase in the Meta
repository, rather than as an external. There are a couple of reasons for this:

• The plugin relies on other code for generating PDFs that is specific to the WordCamp.org environment.
• WordCamp.org has a unified text domain and related project on the WordPress translation site. This version of CampTix Invoices uses the unified domain rather than its own.

The original plugin code is here:
​https://github.com/wceu/camptix-invoices