Add manage button to series blocks

[owi92]

This buttons links directly to the "series details" page. I was considering to only add it to dedicated series pages, but that kinda defeats the purpose of getting there more easily.
The button is only shown if you have write access for that series.

Also includes some refactoring of semi-related code.
To review, probably just ignore individual commits (maybe read the messages tho).

Closes #1594

[dagraf]

Thanks for adding the button. I think, we/you should invest some effort in improving the display of series (especially for smaller screens). What I observed and consider suboptimal:

1. On smaller screens (not on mobile devices) and when metadata is not shown, the buttons stay on the same line but the title is spread across several lines.

2. On smaller screens, when metadata is shown and only in editing-mode, the button to the far right exits the window.

3. When metadata is shown, the buttons are displayed to the right of the description. I would prefer them to be in the upper right corner, next to the title. But that's not a strong opinion.

[owi92]

Thank you for testing, David.

This turned out to be more tricky than expected (which is weird because it looks pretty trivial). I made another proposition in #1618, which fixes the issues that you have observed and moves the buttons to the top. I also removed the "share" and "manage" text, as these should be pretty much understandable without text. That allows some more room for title and decription.
However that is still not perfect and needs some more work if we decide to take that route.

I am also still leaning towards keeping the buttons on the bottom.
It should be noted that the new "manage" button will rarely be seen by regular students, since I do not expect them to have write access to many (if any) series.
I supspect we won't have the time, but if we do, let's briefly talk about this in our next meeting.

[LukasKalbertodt]

Generally looks good to me! I'm fine with omitting the label for those two buttons -- the share button was quite prominent before, it's probably better if it is a bit calmer now.

Regarding the "small screen" problem: I agree with Ole in that I prefer the "buttons below" version, i.e. what we had and what this PR keeps. This PR does rewrite the layout logic for all these elements tho. And while I didn't dig deep into the CSS code, from playing around with the test deployment, it seems that it works well in every scenario! So from my perspective we can keep it like that. I also like the gap reduction from 16 to 8.

Yeah I think that's all my thoughts.