Create a function called theme_by_year that takes as input a year (as an integer) and shows the theme ids and theme names (listed in order by theme id) that were in sets that year.
The column names must be id and name_themes (to differentiate between the name of a theme and the name of a set) in that order.
The index should be reset and go from 0 to n-1.
Each theme should only be listed once even if it appeared in more than one set from that year -- duplicate themes should be based on theme id and not name since there are some themes with the same name but with a different id.
We were supposed to merge the inventory_sets, sets, and theme data which is mainly what I was having the issue with with no duplicates for id
