user.fu support on backend

New methods:
db->users->follow_user
db->users->unfollow_user

Also, db->events->list({ for => $login }) now uses user.fu to choose
appropriate quests
/api/:login/{follow,unfollow} routes
follow/unfollow user button on frontend
quest-completed view shows 0 instead of NaN on first quest
limit Login length to 16 on backend
"follow" button on mobile
limit login input maxlength
email on follow_user
notify_followers option in frontend settings
less ugly newbie-tour styling
user-big view: set active tab on render instead of afterRender
show in dashboard-profile which realms user follows and which users
minor styling of follows dashboard-profile block
current-user model {un,}followUser tests
more jasmine tests; more sinon fakeServers
Merge branch 'follow-users'

http://questhub.io/realm/meta/quest/514e235b91c00fc379000007
rebuild static