Added GroupPinnedStatuses

• Added:
- GroupPinnedStatuses
- controllers for timeline, creation, deletion
- redux actions, reducers for creation, deletion
- timeline fetching in timelines action
- options to pin, unpin in status options popover for group admin

app/models/group_pinned_status.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+# == Schema Information
+#
+# Table name: group_pinned_statuses
+#
+#  id        :bigint(8)        not null, primary key
+#  status_id :bigint(8)        not null
+#  group_id  :bigint(8)        not null
+#
+
+class GroupPinnedStatus < ApplicationRecord
+  belongs_to :group
+  belongs_to :status
+
+  validates_with GroupPinnedStatusValidator
+end