Add description_template to all primitives that don't have one

[tamargrey]

Many primitives that have been added in the last year or two don't have the description_template property specified, resulting in feature descriptions that look like The result of applying NUM_UNIQUE_SEPARATORS to the "favorite_quote".

We should add description_template to all primitives that don't have one specified and add a test that will fail any time a new primitive is added without description_template, forcing devs to either make it an exception or fill out a description_template for new primitives.