regcode 5.x-3.1

Re-release of 3.0 - I think I committed to the wrong branch last time, apologies!

A complete rewrite by danielnolde:

- db-storage with multiple fields, with (per code):
* role granting by code
* expiry of availability
* one-time-only or re-usable codes
* tracking of code-usage (user, date)
* info-column for freestyle-usage
- filter- and order-able code listing / search
- import (with flexible CSV--setting, file-upload- or textarea-import and a default code-data-template)
- permission to override even mandatory regcode-input for adding new users (helpful for admins)

This current development has been sponsored by plazamedia.com