Avoid globally oversighting users with over 1000 edits

Before globally hiding a user, check their edit count
using new function CentralAuthUser::getGlobalEditCount().
If greater than 1000, return a 'centralauth-admin-too-many-edits'
error.

Additionally, cache the result of queryAttached() in the
instance to avoid expensive queries whenever possible.

Bug: 23653
Change-Id: Idd18bde4903c576d56cfede710c0ae4aa09d0d35
Merge "Avoid globally oversighting users with over 1000 edits"