[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

``` SearchText``` was used in the legacy. I took the liberty of renaming it since GET parameters are different in the new stack version since it is using the SF form component (I updated to /content/search as suggested by @lolautruche ):
``` http://ez5.local/content/search?ezdemo_simple_search[searchText]=started&ezdemo_simple_search[save]=&ezdemo_simple_search[ezxform_token]=45d4a4099e0cfa60b919a3003f3e05e9f096bdd8 ```