cubicweb #1955604 [facets] facets are (on average) quite slow [open]

the bigger they are, also the slowest

e.g in a forge ticket list the filter table can take a full second (or more) to compute

or on big /etype lists the same problem arises

hence I propose we load the facets with an ajax request

priorityimportant
typeenhancement
done in<not specified>
load0.500
load left0.500
closed by<not specified>