Enhancement: Search full-text filter

The search result page now has a full-text filter which can be used to filter the displayed files by their content.

https://github.com/owncloud/web/pull/9059
https://github.com/owncloud/web/pull/9087
https://github.com/owncloud/web/pull/9096
https://github.com/owncloud/web/pull/9332
https://github.com/owncloud/web/issues/9058
