Added helper for fetching a specific header from a request.
Added helper for fetching a specific header from a request.

K2InformaticsGmbH/elli,K2InformaticsGmbH/elli,odo/elli,elli-lib/elli,elli-lib/elli,knutin/elli,odo/elli,tsloughter/elli,tsloughter/elli,knutin/elli