search contexts: add search box to single page view

Created by: novoselrok

Add search box to the search contexts single page view with pre-filled current context. Then we need a way of locking the search context dropdown to prevent changing the pre-filled context.

Problem: There is a potential for confusion between a regular full-featured search box and the search notebook query inputs if they appear on the same page. Search box takes you to a separate page once you submit a search, meanwhile search notebooks display the results inline.