Rename and refactor synonyms, & their usage in template code

[waharnum]

'Syonyms' is a bad metaphor for the configuration file at https://github.com/waharnum/inlibraries.com/blob/master/synonyms.json - while it has some synonyms, it's more of a general random substitution lookup file.

The template code for the custom functions is also rather cruddy and excessively tied to the data structure of the file (which might also suck). It's perhaps better to flatten it from the standpoint of the template tags so that custom tags look something like this: {{ random_word_for("types_of_librarians" }}

This one needs some thinking. It also may eventually hit the point where there should be a back end DB or similar.