The "group by" section needs "filter by"

[wenzeslaus]

Filtering should be optional, so no filtering by default.

Filter by:

• Value(s) for any of the basic columns (same choices as for group by)
• Disposition code groups

We can start with one (or two) filter(s) and one value for the selected column/filter like we have for the Timeline which can be filtered by country (and by disposition code group).

We may want to rethink this and add general/common filters all the way at the beginning and let these influence both the group by, the timeline and partially the country plots too.

[mshukuno]

We need to discuss regarding this enhancement. For now, I changed "Group by" section title to "Filter by".