Revert "Revert "Revert "hashtable: introduce a small and naive hashtable"""

This reverts commit 2233efae5396b7fd84235b13234186cda4c5d564.
Revert "Revert "Revert "block,elevator: use new hashtable implementation"""

This reverts commit 14081674f24e703c7717780e175007be3f6f97a0.
Revert "Revert "Remove unused function""

This reverts commit 6a3863e35dea6c90259543b2621bb4bfd76107a3.
Add RNG crypto module