Add featured hashtags to profiles (#9755)

* Add hashtag filter to profiles

GET /@:username/tagged/:hashtag
GET /api/v1/accounts/:id/statuses?tagged=:hashtag

* Display featured hashtags on public profile

* Use separate model for featured tags

* Update featured hashtag counters on-write

* Limit featured tags to 10

config/locales/en.yml

@@ -588,6 +588,10 @@ en:
     lists: Lists
     mutes: You mute
     storage: Media storage
+  featured_tags:
+    add_new: Add new
+    errors:
+      limit: You have already featured the maximum amount of hashtags
   filters:
     contexts:
       home: Home timeline
@@ -807,6 +811,7 @@ en:
     development: Development
     edit_profile: Edit profile
     export: Data export
+    featured_tags: Featured hashtags
     followers: Authorized followers
     import: Import
     migrate: Account migration