Remove reliance on Block properties being public

Remove reliance on Block properties being public

Use getters and setters for $mReason, $mTimestamp, $mExpiry and
$mHideName; use Block::getType to check if a block is an autoblock
instead of checking $mAuto; no change needed for $mParentBlockId,
which is not accessed externally.

Change-Id: I767ed44ce4c2e21f53962d75fb86891add2282f6