Show/hide issue assignee avatar depends on drag-n-drop column in milestone view

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Use same size headers. Add PullReview. Mention shell guide as created by us.
Merge branch 'kanban-fixes' into 'master'

Kanban improvements

When drag from unassigned to assigned column - issue assignee avatar updated
Merge branch 'consistent-headers' into 'master'

Consistent headers