Enhancement: Display search results within files app

We've updated the "Search in all files" view to be displayed within the files app instead of showing them in a dedicated extension.
This way, users don't loose their context and can still use sidebar.

https://github.com/owncloud/web/issues/6496
https://github.com/owncloud/web/issues/6507
https://github.com/owncloud/web/pulls/6511
