Select a coding system release when creating a new codelist/draft

[rebkwok]

Coding systems are now associated with specific releases. Any time that a codelist or codelist version is created, the release needs to be specified.
(Note APIs already require this, see #1401, this issue is about the user-facing options)

• Creating a codelist: opencodelists/views/user_create_codelist.py (/users//new-codelist)
• Creating old style codelist (by uploading CSV): codelists/views/codelist_create.py (codelist//add)
• Creating old style codelist version (by uploading CSV): codelists/views/version_upload.py (codelist///upload-version
• Creating new version (from codelist version page): codelists/views/version_create.py
  - called from templates/codelists/version.html; currently adds the coding system release as a hidden input
  - this is currently just a button on the version page, will need either a new displayed form field, or a popup to select from the available releases (which should be the same one that the current codelist version uses - the current default - or later ones)