Adds several enhancements - see ext. description

[1] Improves search behaviour (todo: make it work with AND, and not OR
between query words). [2] Adds special meta tags for each page, even
OpenGraph (Facebook) tags. [3] Fixes bug when searching for a course in
select2 select boxes the html tags would be presented as results (this
was pretty tricky - see courseSelector helper for details). [4] Fixes
other tiny details.