Update DOIT_SOA_ORDER_IFACE_L to v3

This PR updates the Order Line WSDL to v3. v3 of DOIT_SOA_ORDER_IFACE_L includes two new parameters, P_UNIT_PROMO_PRICE and P_PROMO_DISCOUNT_NAME for specifying promotional discounts.

Project version bumped to 7.0.0, and some Composer dependencies updated. Being in a refactoring mood, I also changed the datatypes in the OrderLineInputParametersMapper to properly reflect the datatype that InputParameters expects (which is really just a cosmetic change since we immediately set the correct values, but this is 'more correct' either way). I plan on doing the same for the rest of the classes and PHP7-ifying the project for its better type hinting, etc.

Please review: @ahoffmann @weizhong-wang @lloyd-carter @KJOYNER