When new member joins a group go to steward selected "welcome" page, if that page is turned on, otherwise go to default home view

[tibetsprague]

• Load new group setting showWelcomePage
• if it is set to true for a group, then when a member joins that group, redirect to /groups/:groupSlug/welcome instead of the home view upon first join (at the end of the GroupWelcome flow)
• the Welcome page is super simple, just displays rich HTML content from new group field welcomePage
• in all views page hide widgets that have visibility === ‘none’