Expose random seed function to scripts

lib/sandbox.js

@@ -54,11 +54,15 @@ class SandboxDate {
 
 function random() {
   if (!state.rng)
-    state.rng = seedrandom(state.sessionContext.timestamp);
+    state.rng = seedrandom(state.sessionContext.deviceId);
 
   return state.rng();
 }
 
+random.seed = function(s) {
+  state.rng = seedrandom(s);
+}
+
 
 class ParameterWrapper {
   constructor(path, attributes, unpacked, unpackedRevision) {