Improve sections/categories/groups dropdown

[ppo]

The bottom-right sections (or categories? groups?) dropdown is not convenient as there are too many items.

Possible solutions (that can be combined):

• Group sections into "section groups" (e.g. letters, emojis, symbols, drawing symbols).
• Open the list in a modal (displayed in sub-categories).
• Use a smart dropdown with search/filter.

Also allow to restrict the list to one or several sections or section groups.
For example, I want to browse all emojis.