Keystore 2.0: Add super encryption infrastructure.

Add super_key.rs a runtime key database for credential based keys and
the relevant metadata fields to the database.

Also in this patch:
* Add DateTime type to represent database wall clock time.
* Move creation time to key metadata.
* Add KeyType field to the keyentry table to accommodate super keys
  and attestation keys.

Test: keystore2_test
Bug: 173545997
Change-Id: I670898174fb0223bf1c910051dfd7ead80b2c1a9
diff --git a/keystore2/src/lib.rs b/keystore2/src/lib.rs
index 45447a9..e13d6c0 100644
--- a/keystore2/src/lib.rs
+++ b/keystore2/src/lib.rs
@@ -28,6 +28,7 @@
 pub mod utils;
 
 mod db_utils;
+mod super_key;
 
 #[cfg(test)]
 mod test {