[#6676] Added registration date to user profile

Signed-off-by: Cory Johns <cjohns@slashdotmedia.com>
[#6795] less mongo queries in trove.children

In my local benchmark of running test_add_remove_label, this
gave a 2.8x speedup
[#6795] single query for trove.children

Additional 5.2x speedup (>14x total) of test_add_remove_label