Remove references to slug on document filter

[beccapearce]

The word slug is not well used by publishers and it is usually the same as the page title. It will be less confusing to users if we just use one.

trello card: https://trello.com/c/Uttw5Q63
Before:

After:

[davidgisbey]

lgtm!

Just a couple of questions

It's still title or slug for statistics announcements. Do you want to update that to or is that out of scope?

The edition filter will still match on title and slug. Do we want to leave that in place?

[beccapearce]

I think it makes sense to update it for both to keep it consistent. but maybe I should double check that that is correct.

And yes The behaviour should stay the same and match on both, people still search by slug so i think we should keep that

[beccapearce]

Just got confirmation that we want to remove all the slug references so it should be removed for stats announcements too :)