Add state param to milestone listing API (#7131)

* Support state params

* update tests

* fix tests

* add state=all support

* update tests

* update swagger

* update swagger

models/fixtures/repository.yml

@@ -8,7 +8,8 @@
   num_closed_issues: 1
   num_pulls: 2
   num_closed_pulls: 0
-  num_milestones: 2
+  num_milestones: 3
+  num_closed_milestones: 1
   num_watches: 3
 
 -
@@ -495,4 +496,4 @@
   num_stars: 0
   num_forks: 0
   num_issues: 0
-  is_mirror: false
+  is_mirror: false