Common utility mixins and use of them in dui/mobile

This pull request contain:

1/ some common widget mixins
2/ some tests for them
3/ the use of the Store/StoreMap mixin in dui/mobile (Storelists)
4/ the change of some dui/mobile tests to comply with new API
5/ the removal of carousel components we decided to remove for now (because they use the old store mechanism and I would have had to recode them for "nothing" if I had kept them).

I have also tested those mixins in a branch of dtreemap (https://github.com/cjolif/dtreemap/tree/experiments)