Add loading spinners to domain/user list pages
Summary: Also display "there are no domains/users in this account" when the list is empty.
Test Plan: `./phpunit --testsuite=Browser"
Reviewers: #hkccp_developers, vanmeeuwen
Reviewed By: #hkccp_developers, vanmeeuwen
Subscribers: #hkccp_developers
Differential Revision: https://git.kolab.org/D1486