Further improvements to search

[enyo]

Now that #302 has landed, there are a few things that can and should be improved:

• lazy loading of the index. gatsby-plugin-local-search is a good source for this
  • Maybe lazy load the individual fields separately
• Maybe use "forward" search for the whole body as well
• Somehow visualise in the results on the site the score when matching.
• When navigating with the arrow keys the results should auto scroll

[HelenaMeyer]

The last parenthesis cannot be seen in "focus":

[HelenaMeyer]

If I search for something that cannot be found, the search page could also have a "Not found" sub-title somewhere in the middle of the page after the search string:

:

[enyo]

@HelenaMeyer both are fixed here #306