Find a way to avoid "removing" anime results when moving an anime to a different season

[Dutchman97]

This is an issue that primarily impacts anime that air/release roughly in-between the different seasons (e.g. Sorairo Utility, ID 1534), where an anime may initially be stored as airing in season X (and be in the season X pre-season survey) but get subbed before the post-season survey of season X-1 goes up - usually that anime will then be moved to season X-1 so that there's no 3-month gap between the anime finishing and users being able to respond with how well they liked an anime (just like with regular seasonals).

Moving an anime from season to season means that responses for that anime essentially disappear from the season it was first in. One potential way of solving this is to store a snapshot of what anime are or should be included in a survey, and using that for the survey form and survey results.