[BZ#779601] Add an empty search state
Submitted by Matthias Clasen
There are some ways to end up with a blank search results page.
For example, select a meal from the popover, and then remote the tag by clicking on the x.
We should present an empty state like we have for empty categories, if this happens. The search page already has such a state, but it is only shown if you type a search string that has no matches. We should re-use it for this case.