Add read only channels

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

...etchat-channel-settings/client/views/channelSettings.html

packages/rocketchat-channel-settings/package.js

...channel-settings/server/functions/saveRoomReadOnly.coffee

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

...es/rocketchat-channel-settings/server/models/Rooms.coffee

packages/rocketchat-lib/i18n/en.i18n.json

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

packages/rocketchat-theme/assets/stylesheets/base.less

...es/rocketchat-ui-flextab/flex-tab/tabs/membersList.coffee

...ages/rocketchat-ui-flextab/flex-tab/tabs/membersList.html

...s/rocketchat-ui-sidenav/side-nav/createChannelFlex.coffee

...ges/rocketchat-ui-sidenav/side-nav/createChannelFlex.html

.../rocketchat-ui-sidenav/side-nav/createCombinedFlex.coffee

...es/rocketchat-ui-sidenav/side-nav/createCombinedFlex.html

...s/rocketchat-ui-sidenav/side-nav/privateGroupsFlex.coffee

...ges/rocketchat-ui-sidenav/side-nav/privateGroupsFlex.html

server/methods/createChannel.coffee

server/methods/createPrivateGroup.coffee

server/methods/joinRoom.coffee