Add schema and DAO for cursors in cloudsql (#370)

* Add schema for Cursor

* Add CursorDao and CursorDaoTest

* Fix comment on getTld

* Change tld column to scope

* Fix cursorTime to be converted to DateTime internally and other small fixes

* Add a CursorType enum and a createGlobal constructor for Cursor

* Rename flyway file

* Use cursorType from common/Cursor.java and add null checks

db/src/main/resources/sql/schema/db-schema.sql.generated

@@ -26,6 +26,14 @@
         primary key (revision_id)
     );
 
+    create table "Cursor" (
+       scope text not null,
+        type text not null,
+        cursor_time timestamptz not null,
+        last_update_time timestamptz not null,
+        primary key (scope, type)
+    );
+
     create table "DelegationSignerData" (
        key_tag int4 not null,
         algorithm int4 not null,