Remove new & edit Admin pages for reimbursement types

These are managed through code (e.g. migrations) rather than the Admin UI.
Leave an index page to display the current state.

Also:
  - Fix a migration. It was failing silently because of cached column information

cherry-picked from f1558b3b454501178a214aefa78eeee08f0c313e in spree master
Add the reimbursement to ReimbursementHelpers.create_creditable params

cherry-picked from efbe926f91e74c0e638a501aaeae203209adee62 in spree master
2-2-dev fix for Spree::Base references

Spree::Base doesn't exist in Spree 2.2