Adding searchtool related language strings to frontend

### Issue
Not really a real issue. I tried to use the new search tools in my component both in backend and frontend. Backend works fine, however in frontend I found some missing language strings.
The `JSEARCH_...` ones are hardcoded in the JLayout and thus can't be adjusted in a 3rd party extension.
The others could be adjusted but could be useful for most 3rd parties anyway.

### Solution
This PR proposes to add some language strings related to search tools to the frontend language file.
They're just copied from backend.

@infograf768 You want to have a look at that :smile: