Integration of the search page to the rest of the App

• Removed dead code related to the old search interface
• Added the possibility to "lock" filters. Locked filters cannot be edited in the filter panel, through the URL, or through the search bar. Locked filters are not affected by the reset and do not get serialized in the URL.
• Added possibility to add a customized header to the search page. It is currently used to display dataset name/DOI when searching within a dataset.
• Now the menu item "Search your data" redirects to a customized entry search page that has the visibility locked to user.
• DatasetPage.js now uses a customized search page with dataset_id locked.