changes to enable mollie support

[magnolia61]

With these changes Mollie is finally working for us.
Reintroduced: getReturnSuccessUrl /
Included: require_once 'CRM/Core/Session.php';
And further some changes to the Mollie library itself.

[eileenmcnaughton]

I'm thrilled this is working for you!

In terms of merging the PR:

1. The changes within the Mollie package need to be done via composer. I see you have been communicating to get them merged upstream. I'm happy to pull in from your fork of the Mollie package rather than the master one while that is resolved but you need to submit a patch to composer.json to do that. (generally people do the composer.json patch PRs & I run composer & commit the results).

The composer.json patch includes where your git repo is ie.

https://github.com/eileenmcnaughton/nz.co.fuzion.omnipaymultiprocessor/blob/master/composer.json#L24

and this line would be changed to dev-master instead of 3.0 where your branch is named master (I think)

https://github.com/eileenmcnaughton/nz.co.fuzion.omnipaymultiprocessor/blob/master/composer.json#L36

You should put that & the processor.mgd file in one PR.

I'm less confortable with the other changes as they affect other processors. I don't understand why the require_once would be needed - if feels like a symptom of another problem - although harmless in itself.

Changing the return url would affect other processors & remove the '2 chances' that they currently have. On the flip side I think Mollie still obviously requires it for some reason.

I think you are at the point where it is finally working for you & that is great and I actually think that leaving this PR open for now is a valid option. We haven't ironed out everything that would allow me to see it as entirely done & dusted - but with this PR here there is definitely enough information for people to get it going and the next person might be able to resolve those last issues.

[eileenmcnaughton]

I'm going to close this because it's stale, but also because I think Mollie might work without extra changes now. I discovered a composer issue causing some Mollie updates to not be in the code base & so the underlying issue is either fixed or moved now...