Move collections to its own foldable section

[cmd-ntrf]

Instead of buttons next to "loaded modules", collections should be its own section, but it should be folded by default.

We could probably use CSS from the extension manager to achieve it.

[cmd-ntrf]

We'll wait for the release of JupyterLab 4.0 before moving forward with this idea.

The amount of code required to build the interface with foldable section like the one used in extension-manager is significantly smaller in 4.0 than it is with 3.x.