Filter schedule entries on picasso by checklist entries

In the french-speaking part of Switzerland, J+S scout camps often have goals (objectifs généraux + spécifiques) on what they want to acheive with the kids during the camp. This seems similar to J+S courses, and this requirement can also be covered with our generic checklist implementation.

However, reportedly, coaches would like to evaluate the selected goals in the picasso, in a visual way. For this reason, we could add a new filtering criterion. The dropdown select should allow to select one or multiple checklist items (or an additional entry "no checklist item"). Then, only schedule entries which contain a checklist material node with one of the selected checklist items should be displayed / highlighted.

This should probably be a multi-select OR filter, just like the progress labels, to make it easier to select a range of checklist items and see all schedule entries where any of them is covered. It is not primarily intended as a search tool to find specific combinations of covered checklist items (like we do it for responsibles), but more of an overview tool to see the distribution of goals over the whole camp.

Other uses: This feature could also benefit courses, although we have already implemented the formally required checklist overview and "list of blocks". Also in some scout camps, people might want to label the coverage of their activities in terms of PBS Beziehungen (relations) using the checklists feature as well. In that case, the evaluation of the balance of Beziehungen in the camp could be made easier as well with this feature.

Open questions:
- When should we highlight schedule entries which don't have a checklist content node at all? Do we need a separate filter option for this? Or is this just equivalent with a checklist content node with no checklist items selected? (Making them different might be useful to make sure all the relevant activities actually have the layout set up properly, as there could be mistakes from copying and pasting activities from older camps / courses.)