Always return default Access-Control-Allow-Headers whitelist

This avoids OPTIONS requests sometimes disallowed because of missing
Access-Control-Allow-Headers, probably due to cached response of
reqeuests without Access-Control-Request-Headers.
Merge pull request #243 from Connexions/add-access-control-allow-headers-whitelist

Always return default Access-Control-Allow-Headers whitelist
Ignore case when checking for english stopwords. Addresses #247
Merge pull request #248 from Connexions/fix-stopwords

Ignore case when checking for english stopwords. Addresses #247
Add route setup tests
Transform legacy module links within collections

Close Connexions/rhaptos.cnxmlutils#73