Make support URL configurable

In self-hosted environments, users may want to point to an internal
website or Wiki for Taiga support.

- Add a configuration option named "supportUrl", akin to
  privacyPolicyUrl and termsOfServiceUrl.
- Set its default to https://tree.taiga.io/support/ to mirror the
  previous behavior.

Fixes #1389.

app/modules/navigation-bar/navigation-bar.directive.coffee

@@ -26,6 +26,7 @@ NavigationBarDirective = (currentUserService, navigationBarService, locationServ
         taiga.defineImmutableProperty(scope.vm, "isEnabledHeader", () -> navigationBarService.isEnabledHeader())
 
         scope.vm.publicRegisterEnabled = config.get("publicRegisterEnabled")
+        scope.vm.supportUrl = config.get("supportUrl")
 
         scope.vm.login = ->
             nextUrl = encodeURIComponent(locationService.url())

app/modules/navigation-bar/navigation-bar.jade

@@ -16,7 +16,7 @@ nav.navbar(ng-if="vm.isEnabledHeader")
             include ../../svg/logo.svg
 
         a(
-            href="https://tree.taiga.io/support/",
+            href="{{ vm.supportUrl }}",
             target="_blank",
             title="{{'PROJECT.NAVIGATION.HELP_TITLE' | translate}}",
             translate="PROJECT.NAVIGATION.HELP"

conf/conf.example.json

@@ -11,6 +11,7 @@
     "defaultTheme": "taiga",
     "publicRegisterEnabled": true,
     "feedbackEnabled": true,
+    "supportUrl": "https://tree.taiga.io/support",
     "privacyPolicyUrl": null,
     "termsOfServiceUrl": null,
     "maxUploadFileSize": null,