Closes #15649

See #17478

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

This will be useful when you want to ask for the 
number of items and later iterate over them, without 
needing to ask if the association is load or not.

So you avoid extra database queries

Use the project finder in the todos finder to limit todos to just ones within projects you have access to.

By joining the Todos on the project table.

Signed-off-by: NRémy Coutable <remy@rymai.me>

When the group is the default blank icon, this needs to use the
`image_path` helper; otherwise, the link won't work if assets are
precompiled. This still works fine for uploaded icons in either case.