move getAuthz and getBuildmaster to ContextMixin

ContextMixin depends on getAuthz, after all.  Fixes #963

master/buildbot/status/web/base.py

@@ -180,6 +180,13 @@ def getStatus(self, request):
     def getTitle(self, request):
         return self.title
 
+    def getAuthz(self, request):
+        return request.site.buildbot_service.authz
+
+    def getBuildmaster(self, request):
+        return request.site.buildbot_service.master
+
+
 class HtmlResource(resource.Resource, ContextMixin):
     # this is a cheap sort of template thingy
     contentType = "text/html; charset=utf-8"
@@ -236,12 +243,6 @@ def render(self, request):
             return ''
         return data
 
-    def getAuthz(self, request):
-        return request.site.buildbot_service.authz
-
-    def getBuildmaster(self, request):
-        return request.site.buildbot_service.master
-
 
 class StaticHTML(HtmlResource):
     def __init__(self, body, title):