Allow user to select which dictionaries to display when reading

[nramos0]

Story

• As a normal user, I can pick which dictionaries will be shown in the definition search while reading, so that I can freely search up words in any dictionary and customize which dictionaries I want to use.

Definition of Done

• The dictionaries that show up in the definition search box should no longer be dependent on the user's display language. The display language should not at all affect which dictionaries are shown, though the study language still does, since a given dictionary must have either end be the study language of the current article being read.

[nramos0]

The first step to this is displaying all possible dictionaries for a language pair (chinese-english, chinese-chinese for studying chinese, english-chinese, english-english for studying english) and allowing the user to statically hide or show any particular one. The second step of persisting this preference to the database wouldn't be too big of an additional task.