Using a better approach to cachebusting for the asset picker prefetch

Instead of setting a TTL, add a cachebuster to the prefetch URL that is based on the last modified date of the asset data.

Bloodhound, the search engine we are using for the uber select, defaults to using the URL as the unique cache key and so whenever a file is edited uploaded, all the prefetch local caches will be busted and clients will always have an up to date list

[skip ci]
Using the same cachebusting technique for the asset picker on all default object pickers
Removing CKEditor from the main repo - planning on maintaining the editor separately

[skip ci]
Putting back the preside custom editor plugins into the main repository

This way, we just have the preside extensions to CKEditor in our repo

[skip ci]
Ignore built CKEditor files that will find there way in this directory - except for ckeditor custom config + plugins
Adding pulling down of CKEditor into the local build script
Having custom CKEditor work for preside live in a separate directory

This is easier to manage and clearer to maintain