Merge branch 'master' into glitch-soc/merge-upstream

Conflicts:
- app/controllers/admin/base_controller.rb
  Some refactoring made upstream, no real conflict.
- app/javascript/mastodon/features/compose/components/compose_form.js
  Updated using upstream's code but using maxChars instead of the
  hardcoded length of 500 characters per toot.
- app/javascript/styles/mastodon/components.scss
  Upstream redesigned the onboarding modal. Not sure why we had a
  conflict there.

Gemfile.lock

@@ -251,7 +251,7 @@ GEM
     hamster (3.0.0)
       concurrent-ruby (~> 1.0)
     hashdiff (0.3.7)
-    hashie (3.5.7)
+    hashie (3.6.0)
     heapy (0.1.4)
     highline (2.0.0)
     hiredis (0.6.3)
@@ -345,7 +345,7 @@ GEM
     mime-types-data (3.2018.0812)
     mimemagic (0.3.2)
     mini_mime (1.0.1)
-    mini_portile2 (2.3.0)
+    mini_portile2 (2.4.0)
     minitest (5.11.3)
     msgpack (1.2.4)
     multi_json (1.13.1)
@@ -356,8 +356,8 @@ GEM
       net-ssh (>= 2.6.5)
     net-ssh (5.0.2)
     nio4r (2.3.1)
-    nokogiri (1.8.5)
-      mini_portile2 (~> 2.3.0)
+    nokogiri (1.9.1)
+      mini_portile2 (~> 2.4.0)
     nokogumbo (2.0.0)
       nokogiri (~> 1.8, >= 1.8.4)
     nsa (0.2.4)
@@ -366,8 +366,8 @@ GEM
       sidekiq (>= 3.5.0)
       statsd-ruby (~> 1.2.0)
     oj (3.7.4)
-    omniauth (1.8.1)
-      hashie (>= 3.4.6, < 3.6.0)
+    omniauth (1.9.0)
+      hashie (>= 3.4.6, < 3.7.0)
       rack (>= 1.6.2, < 3)
     omniauth-cas (1.1.1)
       addressable (~> 2.3)
@@ -712,10 +712,10 @@ DEPENDENCIES
   microformats (~> 4.0)
   mime-types (~> 3.2)
   net-ldap (~> 0.10)
-  nokogiri (~> 1.8)
+  nokogiri (~> 1.9)
   nsa (~> 0.2)
   oj (~> 3.7)
-  omniauth (~> 1.2)
+  omniauth (~> 1.9)
   omniauth-cas (~> 1.1)
   omniauth-saml (~> 1.10)
   ostatus2 (~> 2.0)