Add rough draft of repeating timelock contract

src/test/contracts/timelock_repeat.mligo

@@ -0,0 +1,20 @@
+type storage = {
+  last_use: timestamp;
+  interval: int;
+  execute: unit -> operation list;
+}
+
+let main (p,s: unit * storage) : operation list * storage =
+  if Current.time > (s.last_use + s.interval)
+  then
+    let s: storage = {
+                      last_use = Current.time;
+                      interval = s.interval;
+                      execute = s.execute;
+                      }
+    in
+    (s.execute (), s)
+  else
+    (* TODO: Add the time until next use to this message *)
+    (failwith "You have to wait before you can execute this contract again.":
+       operation list * storage)