Replace use of contributeMode with alternatives

Replace use of contributeMode with alternatives

This addresses 2 places contributeMode is used

1)  CRM_Contribute_BAO_Contribution::createAddress does not require this check - it
works by checking if there are appropriate params from the billing profile - which
will have been displayed on the form or not as required by the processor

2) Replaces a specific check for paypal express with a check specific to that
class name. In the process functions are added for getPaymentProcessorValue()
in keeping with recently added getEventValue() getParticipantValue() etc