UX: improved our footer handling

- new "show-footer" mixins
- converted most of the routes to ES6
- FIX: handling of "indexStream" in user pages

There will now be a footer on all the following pages
- /exception
- /about
- /latest
- /new
- /unread
- /starred
- /top
- /categories
- /c/:category
- /c/:category/l/latest
- /c/:category/l/new
- /c/:category/l/unread
- /c/:category/l/top
- /t/:topic/:id
- /groups/:name/members
- /user/activity
- /user/activity/topics
- /user/activity/posts
- /user/activity/replies
- /user/activity/likes-given
- /user/activity/likes-received
- /user/activity/bookmarks
- /user/activity/starred
- /user/badges
- /user/notifications
- /user/flagged-posts
- /user/deleted-posts
- /user/private-messages
- /user/private-messages/mine
- /user/private-messages/unread
- /user/invited
- /user/:username/preferences
- /faq (static pages)
- /badges
- /badges/:id/:badge