Rewrite folder module and migrate to new collection API.

[lgetwan]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

The folder module was still a bit oldschool spaghetti code.

What is the new behavior?

The folder module now uses the new API

[msekania]

@lgetwan,

First of all, the restructured module looks great.

As for #533, I would say that it is more of a feature request.
I think I have implementation almost ready. If there is no other implementation or plans (like keeping it tight to REST API behavior), I can make PR with changes to this PR or wait until this PR is accepted and make my PR after that.

[robin-checkmk]

@msekania I think it makes sense for you to open your PR based on this branch. That way, we can either merge your changes into this branch, or we merge this PR, which will make your PR automatically move to the devel branch. Either way will it make things easier, when we can see the actual code.

[msekania]

@robin-checkmk,

I made a PR, see #539 , but there are some merge issues.
Could you please have a look.
Thanks

[robin-checkmk]

@msekania thanks for the PR! I think @lgetwan has to take a look at the conflict. Are you sure, you based your changes on the top of this branch?

[msekania]

@robin-checkmk, yes, let's wait for @lgetwan.

I sync and pulled this branch before branching out to mine.
Conflicts also look "interesting". Should not be an issue.

[lgetwan]

Thanks for creating this pull request, @msekania!
This week, I'm quite busy, also in the first half of next week. I will try to resolve the merge conflicts until end of next week.

[lgetwan]

I will close this PR, as its complete contents were already merged into #539, where they have been improved further.