Only reindex in development

# Why?

 * For convinience, we were reindexing the `Crop` model in development mode
 * This inadvertently was causing excessive reindexing on production and staging, leading to slow deploys and one-off production commands.

# What Changed?

 * Added `Guide` to the list of models to be indexed
 * Moved it into `development.rb` so it doesn't affect production