feat: Disable attachments and emoji picker in the web widget (#1102)

Signed-off-by: Pranav Raj Sreepuram <pranavrajs@gmail.com>

db/migrate/20200730080242_add_feature_setting_to_website_inbox.rb

@@ -0,0 +1,5 @@
+class AddFeatureSettingToWebsiteInbox < ActiveRecord::Migration[6.0]
+  def change
+    add_column :channel_web_widgets, :feature_flags, :integer, default: 3, null: false
+  end
+end