v3.23.1: the PLI dictionary defaults and the PLI codec tag fixes

An unconfigured PLI dictionary answered result-ok with no data object,
which confuses applications that expect data.  The dictionary now has a
base layer of sensible defaults for the qualifiers the pinned ETSI specs
define (TS 102 223 8.x, tags per TS 101 220 V18.3.0 Table 7.23):

- location as the test network 001/01 + LAC 0000 (8.19),
- the classic test IMEI 490154203237518 as F-padded BCD (8.20) and its
  IMEISV (8.74),
- language 'en' (8.45), Timing Advance (2E/AE), E-UTRAN (8.61; UTRAN +
  E-UTRAN for the multiple-technology qualifier 0E),
- automatic search mode (8.75), a full battery (8.76).

An override set through /api/pli-dict wins, and clearing a field restores
its default (the PWA's Save re-renders the effective values; the GET returns
the override or the default for the full qualifier set).  The date/time
qualifier stays empty so the host clock keeps answering it; the
3GPP/3GPP2-specific qualifiers (NMR, ESN, MEID, CSG/HNB, WLAN, slices,
CAG, ...) stay empty - the ETSI specs define no contents for them, and a
fabricated object would mislead the application more than no answer.

Verifying the values against the pinned tag table exposed pre-existing bugs
in the PWA's PLI inline codecs, fixed here:
- Timing Advance used C6 (a 3GPP2 tag) -> 2E/AE;
- IMEISV used 94 (the IMEI tag) -> 62/E2;
- Network Search Mode used AD (the Language tag) -> 65/E5, and its labels
  were swapped ('00' Manual / '01' Automatic per 8.75);
- the battery field was a percentage where 8.76 is an enum ('00' very low
  ... '04' full, 'FE'/'FF');
- encImeiPli padded the odd 15th digit with 0 instead of F (TS 124 008).

Docs: help EN/RU, api.md, the guide.  Tests: the defaults + the resolution
order (Python), the HTTP endpoint's defaults/override/clearing, the codec
tags/labels and a server-defaults drift guard (Node).  846 frontend +
829 Python; sw cache simple-v414.

tests/test_fetch_routes.py

@@ -115,6 +115,57 @@ if __name__ == '__main__':
     unittest.main()
 
 
+class PliDictHttpTests(unittest.TestCase):
+    """The PLI dictionary's defaults, overrides and clearing (v3.23.1)."""
+
+    def setUp(self):
+        self.server = _build_http_server('127.0.0.1', 0, PysimHandler)
+        self.server.log_requests = False
+        self.server.app = None
+        threading.Thread(target=self.server.serve_forever, daemon=True).start()
+        self.port = self.server.server_address[1]
+
+    def tearDown(self):
+        self.server.shutdown()
+        self.server.server_close()
+
+    def _req(self, method, path, body=None):
+        data = json.dumps(body).encode() if body is not None else None
+        req = urllib.request.Request(
+            'http://127.0.0.1:%d%s' % (self.port, path), data=data,
+            headers={'Content-Type': 'application/json'}, method=method)
+        try:
+            with urllib.request.urlopen(req, timeout=5) as res:
+                return res.status, json.loads(res.read() or b'{}')
+        except urllib.error.HTTPError as e:
+            return e.code, json.loads(e.read() or b'{}')
+
+    def test_defaults_overrides_and_clearing(self):
+        import pysim_simple_server.server as srv
+        try:
+            status, resp = self._req('GET', '/api/pli-dict')
+            self.assertEqual(status, 200, resp)
+            self.assertEqual(resp['00'], '930500F1100000')
+            self.assertEqual(resp['0A'], '630104')
+            self.assertEqual(resp['03'], '')      # the host clock answers it
+            self.assertEqual(resp['02'], '')      # no default
+            status, resp = self._req('POST', '/api/pli-dict',
+                                     {'01': '94080000000000000000'})
+            self.assertEqual(status, 200, resp)
+            self.assertEqual(resp['01'], '94080000000000000000')
+            self.assertEqual(srv._PLI_DATA.get(0x01), '94080000000000000000')
+            # clearing the field restores the default
+            status, resp = self._req('POST', '/api/pli-dict', {'01': ''})
+            self.assertEqual(status, 200, resp)
+            self.assertEqual(resp['01'], srv.PLI_DEFAULTS[0x01])
+            self.assertNotIn(0x01, srv._PLI_DATA)
+            # a bad value is ignored
+            status, resp = self._req('POST', '/api/pli-dict', {'01': 'ZZ'})
+            self.assertEqual(resp['01'], srv.PLI_DEFAULTS[0x01])
+        finally:
+            srv._PLI_DATA.pop(0x01, None)
+
+
 class CardFreeGetTests(unittest.TestCase):
     """Cached GETs must answer while the card lock is held.