* Fix "?q=test&engines=wikipedia": fix exception
* Fix "?q=test&engines=wikipedia&categories=images": now the engines from images category are included.
* Fix parse_timeout: make sure a value is always returned
* Various typing fixes (searx.webadapter, searx.search.SearchQuery)
was previously a Dict with two or three keys: name, category, from_bang
make clear that this is a engine reference (see tests/unit/test_search.py for example)
all variables using this class are renamed accordingly.