Add site-wide search

This adds site-wide search so that one can search the docs, projects and other pages. Because we are limited by Jekyll and can't do any processing on the server, I decided to make it a fast as possible by dynamically loading the search page (which I can change if it feels weird). Once we get more documentation migrated, I think being able to search will make it a lot easier to find useful docs.
The name "content-wrapper-for-sidebar" is a bit misleading - although I can't think of any good names that don't take up half the page.