Merge pull request #413 from glogiotatidis/invite

Invite fixes
Merge pull request #408 from glogiotatidis/incomplete-profiles

Incomplete profiles
Merge pull request #412 from glogiotatidis/827514

[fix bug 827514] Allow sorting users based on country, voucher and is_vouched.
[fix bug 843583] Do not list non-vouched users in search or groups by default.