When the user choose "Auto-detected", the choice remains on the following queries.
The detected language is displayed.
For example "Auto-detected (en)":
* the next query language is going to be auto detected
* for the current query, the detected language is English.
This replace the autodetect_search_language plugin.
Most engines that support languages (and regions) use the Accept-Language from
the WEB browser to build a response that fits to the language (and region).
- add new engine option: send_accept_language_header
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>