Allow multiple instances of keystone

Continuation of #1775. Let’s track our progress here, @snowkeeper @JedWatson

So for the time being all that needs to happen is for instance in List, instead of var keystone=require('../'); we want to make it like this (as you already suggested @jed):

  module.exports = function(keystone){
      //do something with    keystone
  } 

My suggestion for now is that we ​_do_​ leave the circular dependencies. We rewrite all the keystone dependents to use a closure as above.

I think these are the files that need to be updated and obviously also wherever they are required, not including tests:

• admin/server/api/cloudinary.js
• admin/server/api/counts.js
• admin/server/api/download.js ???
• admin/server/api/item/delete.js
• admin/server/api/item/get.js
• admin/server/api/list/delete.js
• admin/server/api/list/download.js
• admin/server/api/s3.js
• admin/server/api/session/signin.js
• admin/server/api/session/signout.js
• admin/server/routes/home.js
• admin/server/routes/item.js
• admin/server/routes/list.js
• admin/server/routes/signout.js
• fields/types/cloudinaryimage/CloudinaryImageType.js
• fields/types/cloudinaryimages/CloudinaryImagesType.js
• fields/types/location/LocationType.js
• lib/content/index.js
• lib/content/page.js
• lib/email.js
• lib/list.js
• lib/list/register.js
• lib/list/relationship.js
• lib/schemaPlugins/history.js
• lib/schemaPlugins/methods/getRelated.js
• lib/schemaPlugins/track.js
• lib/session.js
• lib/updateHandler.js
• lib/updates.js
• lib/view.js

All changes should be pushed to the prototype branch. Also, don’t forget to rebase on top of master!

IMPORTANT: wherever a file only uses a dependency of keystone, please inject the dependency directly, if possible. E.g. admin/server/api/counts.js only uses keystone.lists, i.e. I’ll be injecting lists instead of keystone.

[JedWatson]

Unfortunately this got really out of date… I’ve picked it up in much smaller pieces and am working through the remaining bits. Will tag this issue in my commits, but basically going to do this bit by bit (and ensure everything works with individual commits going forward in master) rather than try and branch then merge a big PR.

[gautamsi]

Keystone 4 is going in maintenance mode. Expect no major change. see #4913 for details. Keystone v5 is modular and flexible, see if it helps, if not open issue there.