Skeleton for delegate with setters for different credentials
Token-requesting-chain
Inline-documentation for token-request-chain
add ability to clear credentials to delegate
clear credentials when auth-headers are cleared
oauth2delegate: dispatch auth-chain and wait for it to finish
bugfix: remove recursion when setting fail-block
bugfix: strong retain on delegate
dispatch getting headers to allow the delegate to get them asynchronously
fix waiting for token
TODO: if several parallel requests fail at the same time, don't refresh the token for each of them.
CONSIDER: put the handling of parallel fails into the client or the delegates?
Merge branch 'feature/OAuth2Delegate' into develop