Add an option for appending trailing slash

[shangxiao]

Django will redirect if missing trailing slashes, but this will only work for GET. Redirects will also not work if doing a cross origin request while developing (eg localhost:4000 -> localhost:8000)

[shangxiao]

Some more info: I tried removing the trailing slashes from my DRF router, however there are assumptions in amygdala that the urls specified in the schema config will always have a trailing slash: https://github.com/lincolnloop/amygdala/blob/master/amygdala.js#L130