Less toolbar spacing option

[InAnYan]

Closes https://github.com/JabRef/jabref-issue-melting-pot/issues/561.

What do you think?

New UI:

Toolbar:

Setting:

Old UI:

Mandatory checks

- [ ] Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
- [ ] Tests created for changes (if applicable)

• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

We really need a restart? ^^

[koppor]

We should not offer a switch for that. Either CSS skinned or find a proper default.

Proposal:

1. Work on https://github.com/JabRef/jabref-issue-melting-pot/issues/558.
2. Add switch "compact UI", where everything is set

Reason: For me: Too much code / preferences for a tiny change 😅

[calixtus]

Can this matter be somehow transfered entierly to css? It would be great if we only had basic controls hardcoded and all the styling (i mean really all the styling options) controlled by css - which would make it really user-modifieable and less clumsy in the java sources...

[InAnYan]

Well, yeah)

I only understood this i in the end, that we can use some CSS setting, rather this.

Closing in favour of the mentioned issue

[calixtus]

Im thinking, maybe one could give the spacers a name, then they probably would be accessible from css? I'm not sure if this is possible...