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.rb

@@ -36,6 +36,9 @@ class Group < ApplicationRecord
   has_many :group_accounts, inverse_of: :group, dependent: :destroy
   has_many :accounts, through: :group_accounts
 
+  has_many :group_pinned_statuses, inverse_of: :group, dependent: :destroy
+  has_many :pinned_statuses, source: :status, through: :group_pinned_statuses
+
   has_many :group_removed_accounts, inverse_of: :group, dependent: :destroy
   has_many :removed_accounts, source: :account, through: :group_removed_accounts