Lists (#5703)

* Add structure for lists

* Add list timeline streaming API

* Add list APIs, bind list-account relation to follow relation

* Add API for adding/removing accounts from lists

* Add pagination to lists API

* Add pagination to list accounts API

* Adjust scopes for new APIs

- Creating and modifying lists merely requires "write" scope
- Fetching information about lists merely requires "read" scope

* Add test for wrong user context on list timeline

* Clean up tests

spec/fabricators/list_account_fabricator.rb

@@ -0,0 +1,5 @@
+Fabricator(:list_account) do
+  list    nil
+  account nil
+  follow  nil
+end

spec/fabricators/list_fabricator.rb

@@ -0,0 +1,4 @@
+Fabricator(:list) do
+  account nil
+  title   "MyString"
+end