[WIP] EZP-21527: Simple search with platform stack

Link: https://jira.ez.no/browse/EZP-21527

## Status
This issue still has a lot of todos left. Feedback is welcome and if you have leads on how to solve the technical todos, feel free to comment.

## TODO
- [ ] Handle request caching
- [ ] Modify the search for in the header of the page to call the new stack search
- [ ] Cleaner redirect on success
- [ ] Add GET param from the form in the pager fanta urls (previous, next, etc)
- [ ] Find the best way to display the advanced search URL (currently a bit hackish)
- [ ] Can we display words excluded from the search ?
- [ ] Remove debug values from config files

You probably don't need to use `$this->get( 'ezdemo.form.type.simple_search' )` as you aliased the type. Just use `'ezdemo_simple_search'`.