add a token to fetch urls requiring image resize/crop to prevent external DDOS via fetch
refactor fetch to support unittesting
code changes in the rest of the code base to support testing fetch
extend TestRequest class to test fetch & detail; add a test to check it does
update TestResponse class to return specific headers & status codes (with tests)
add test for fetch using image tokens
add some dependency checks with test skips to fetch tests and tests which use TestResponse::headers
Merge pull request #203 from splitbrain/fetchissues3

prevent third-party requests from using fetch