QAbstractOAuth{,2} use virtual methods for no good reason

These classes declare a few methods as virtual while there doesn't seem to be any reason for the methods to be virtual:

• QAbstractOAuth::clientIdentifier: just return whatever has been set with setClientIdentifier()
• QAbstractOAuth::setClientIdentifier: just store the string in the private structure
• QAbstractOAuth::token and QAbstractOAuth::token: same as above
• QAbstractOAuth2::responseType: add a (protected?) setResponseType() method and just return the value set with that method.