feat: isolated client class to allow for parallel usage + extension mocking

[daniel-sc]

Hi all,

the issues with the static Podio class were nagging me since long - with this change, we should have better architecture. I admit that this is a large code change and of course a breaking change for users, but the following improvements are worth it from my perspective:

• Easy handling of multiple/parallel logins/authentications (simply create multiple instances of PodioClient)
• Easy extension (you can subclass PodioClient to alter behavior)
• Easy mocking/stubbing (now it would be feasible to unit test a "save" method..)

Please take this PR as a basis for discussion, if you think this could be done better or should not be done at all, I'm happy about any feedback!

closes #90
BREAKING CHANGE: replace static Podio with instantiable PodioClient

[daniel-sc]

@carlfredrikhero @rafaelmb @bajarang-agarwal @timosillander @dylannadon anyone any inputs? (as noted before, I'm happy to deal with critical feedback ;) )

[rafaelmb]

LGTM!

[bajarang-agarwal]

@daniel-sc
Thank you for sharing your idea and making this large change. I agree that having a static class is really not good and the new approach is going to improve things a lot. You really spent a long time to get this right.

This is a major breaking change and it will impact a large number of users. I am fully not 100% sure whether we should make a big breaking change or not. So I am happy to hear the feedback from other community members.

I have not tested the PR but in review, this looks good to me.

[daniel-sc]

@bajarang-agarwal Completely agree!

To facilitate a smooth transition we could make a beta release. Then we and other users could test and provide feedback on problems?

I'd suggest to first merge and then create the beta release (from master). But I'm not 100% sure, what do you think?

Should we wait some more, or should we proceed?

[bajarang-agarwal]

@daniel-sc
I completely agree with the beta release, you can proceed with merging and making the beta release.