Rather than having to do DatabaseBlock calls directly,
and then ManualLogEntry calls to facilitate logging,
let's create a BlockUser service, capable of blocking users
and logging, optionally with permission checking.
This should make blocking users easier for developers,
for instance, AbuseFilter or CheckUser can easily
benefit from this commit.
Bug: T189073
Change-Id: Ifdced735b694b85116cb0e43dadbfa8e4cdb8cab
