[fix] startpage engine: language/region & time support & fix CAPTCHA

One reason for the often seen CAPTCHA of the startpage requests are the
incomplete requests SearXNG sends to startpage.com.  To avoid CAPTCHA we need to
send a well formed HTTP POST request with a cookie, we need to form a request
that is identical to the request build by startpage.com itself:

- in the cookie the **region** is selected
- in the POST arguments the **language** is selected

Based on the *engine_properties* boilerplate, SearXNG's startpage engine now
implements a `_fetch_engine_properties()` function to fetch regions & languages
from startpage.com.

This patch is a complete new implementation of the request() function, reversed
engineered from the startpage.com page.  The new implementation adds

- time-range support
- save-search support

to the startpage engine which has been missed in the past.

The locale code 'no_NO' from startpage does not exists and is mapped to nb-NO.
For reference see languages-subtag at iana [1], `no` is the macrolanguage::

     type: language
     Subtag: nb
     Description: Norwegian Bokmål
     Added: 2005-10-16
     Suppress-Script: Latn
     Macrolanguage: no

Additional hints:

- To fetch languages from startpage, this patch makes use of the
  EngineProperties implemented in 7bf0d46c

- Te get Startpage's locale & language, the function get_engine_locale from
  9ae409a is used.

[1] https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry
[2] https://www.w3.org/International/questions/qa-choosing-language-tags#langsubtag

Closes: https://github.com/searxng/searxng/issues/1081
Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/autocomplete.py

@@ -11,9 +11,9 @@ from lxml import etree
 from httpx import HTTPError
 
 from searx import settings
-from searx.data import ENGINES_LANGUAGES
 from searx.network import get as http_get
 from searx.exceptions import SearxEngineResponseException
+from searx.engines import engines
 
 # a _fetch_supported_properites() for XPath engines isn't available right now
 # _brave = ENGINES_LANGUAGES['brave'].keys()
@@ -110,9 +110,11 @@ def seznam(query, _lang):
 
 def startpage(query, lang):
     # startpage autocompleter
-    lui = ENGINES_LANGUAGES['startpage'].get(lang, 'english')
+    engine = engines['startpage']
+    _, engine_language, _ = engine.get_engine_locale(lang)
+
     url = 'https://startpage.com/suggestions?{query}'
-    resp = get(url.format(query=urlencode({'q': query, 'segment': 'startpage.udog', 'lui': lui})))
+    resp = get(url.format(query=urlencode({'q': query, 'segment': 'startpage.udog', 'lui': engine_language})))
     data = resp.json()
     return [e['text'] for e in data.get('suggestions', []) if 'text' in e]