This commit fixes two bugs:
- 'quick_create' is a special value for the on_create option, it is not an
action xmlid. So when this option is set either in a ungrouped or in an
empty grouped Kanban view, we should try to execute 'quick_create'.
- the 'create' button is muted (btn-default instead of btn-primary) in
grouped Kanban with no column. This status should be updated at each
do_search, and each time a column is added/deleted.