[ON PROD] multiuser: build and integrate project switcher

[kolbinski]

@altsang Ready for tests on staging under feature flag: http://staging.lunchbadger.com/?multiuser

Header menu has:

• new button Manage projects with only one option now: Switch project
• logout button is replaced with Profile button, where we can see, who is logged in + old Logout functionality

Shared projects are simulated for now - each user can switch between those usernames: al, al2, ko and sk.

[altsang]

this look great, reviewed on staging