[IMP] project: remove doc count on project kanban view and optimize task count

This commit removes document count on project kanban view. Indeed it
does not add much valuable information and bloats the kanban cards.

In order to keep the kanban card order, it was required to adapt all
inherited views. The order is 'task', 'issue', 'rating', 'timesheet'
and 'forecast'.

It also uses a read_group to better compute task count, by the way.