BO32 - Add the capability to change Sponsorship levels' order

[gregoriopalama]

Modify the buttons added in #189 to change the order of a Sponsorship level.
When a level is the first in the list, then the "Put up" button must be disabled.
When a level is the last in the list, then the "Put down" button must be disabled.

Make sure that the list in the page is ordered by the position field for each sponsorship level.

When a level's position is changed by clicking on a button, we will have 2 levels that need the position to change. The call to the Sponsorship API to update the position must be done for the level with the lowest position value: this is because the endpoint will update the position for the other level too.

Depends on #183 and #189.