Fixes to notification email about joining organization

This is work for https://aptivate.kanbantool.com/boards/5986-econsensus#tasks-1257223

(This pull request is a replacement for https://github.com/aptivate/econsensus/pull/140. I had thought that pushing to a branch that was already the subject of a pull request would update that request, but this didn't happen this time - hence the new request.)