corrected OID of SignedData (length byte was in value field)
Merge pull request #14 from PersoSim/personalizationfix

corrected OID of SignedData (length byte was in value field)
AbstractTaProtocol: Add hasChallenge()
DefaultTaProtocol: Handle Get Challenge as first step correctly

Get Challenge was already accepted as the first step. The TR-03110-3
section B.3. doesn't elaborate on this, but it should be safe to
interpret the phrasing ("... i.e. the ICC MUST keep a generated
challenge upon usage by External Authen­ticate...") to mean that step
4 is omitted in this case, particularly since a second Get Challenge
doesn't make much sense.