adapt to new SW360 release

[gernot-h]

From a comment by @heliocastro in #14 (comment):

Just FIY, we're in full mode towards next SW360 release, where we we kicked away liferay and whole authentication methods changed and extended API calls will exist, so some refactoring will be needed on sw360python as well.
( Yes, i'm willing to help as well )

[t-graf]

@gernot-h please have a look at the branch 34-adapt-to-new-sw360-release.
Do we need more?

[gernot-h]

I don't have access to our v20 server yet and as our test instance will be switched anyways next week, I planned to look into the changes next week, would that be still in time for you? In the meantime, I'd suggest to create a PR from your branch, probably marked as draft, so that other users will notice it quickly. By the way, I think we should mention v20 explicitly in the ChanegLog.