Refactor/passconfig

Added an optional $config parameter to PayFlowAPI so the config can be optionally passed in as an array. It is written so that if nothing is passed in it will be loaded from the original config file.
The validation_parameters field was also added to the PayFlowAPI class since all of its child classes use it.

Some changes are newline differences. Sorry for the unnecessary diffs due to that. There seems to be two different newline styles in the code. It would probably be a good idea to due a reformat to avoid this in the future.