Replace SysCache with HashtableCache

It looks like SysCache has a bug with EvictEntity, the the commit
94402f3428b50f65dd5720182bfce5fe29aede01 appeared because cache provided
by SysCache didn't clear properly, it worked when I replaced the
EvictEntity(typeof(Blog).FullName) with
EvictEntity(typeof(Blog).FullName, 2), the logs reported that they
evicted all Blogs, but immediately later  hit the cache.