added default field

...-messages/client/views/channelSettingsMailMessages.coffee

...il-messages/client/views/channelSettingsMailMessages.html

...chat-channel-settings/client/views/channelSettings.coffee

...t-channel-settings/server/methods/saveRoomSettings.coffee

packages/rocketchat-lib/server/models/Rooms.coffee

...ages/rocketchat-ui-admin/admin/rooms/adminRoomInfo.coffee

packages/rocketchat-ui-admin/admin/rooms/adminRoomInfo.html

packages/rocketchat-ui-admin/admin/rooms/adminRooms.coffee

...cketchat-ui-admin/admin/rooms/channelSettingsDefault.html

...rocketchat-ui-admin/admin/rooms/channelSettingsDefault.js

packages/rocketchat-ui-admin/package.js

packages/rocketchat-ui-admin/publications/adminRooms.js