fix(web): embed challenge ID in pass-challenge invocations (#944)

* refactor: make challenge pages return the challenge component

This means that challenge pages will return only the little bit that
actually matters, not the entire component.

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(web): move Anubis version info to be implicitly in the footer

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(web): embed challenge ID into generated pages

Signed-off-by: Xe Iaso <me@xeiaso.net>

* fix(lib): make tests pass

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib/policy/config): amend tests

Signed-off-by: Xe Iaso <me@xeiaso.net>

* test(lib): fix tests again

Signed-off-by: Xe Iaso <me@xeiaso.net>

---------

Signed-off-by: Xe Iaso <me@xeiaso.net>
Signed-off-by: Xe Iaso <xe.iaso@techaro.lol>

lib/policy/config/config_test.go

@@ -109,7 +109,7 @@ func TestBotValid(t *testing.T) {
 				Action:    RuleChallenge,
 				PathRegex: p("Mozilla"),
 				Challenge: &ChallengeRules{
-					Difficulty: 0,
+					Difficulty: -1,
 					ReportAs:   4,
 					Algorithm:  "fast",
 				},