[FIX] gamification, website_{profile, slides}: correctly display next rank

This fix correctly displayed motivational of next rank to achieve depending
on current karma. Indeed description_motivational field is not the
motivational to reach next rank but to reach the current rank, taken from
previous rank point of view. That way a given rank is configured by modifying
only 1 data.

When not having any karma points (newly created user) the next rank is computed
as being the first available rank. Motivational phrases and badges are updated
accordingly. This commit partially reverts 489c8623.

Result

  * new user with no karma: next rank is the first rank;
  * user with karma and next rank: as currently;
  * user being at final rank: next rank is just current rank with a 100%
    circle;

Linked to task 2005840
Related to PR #34220