Create new "transition" mod, add untested fn

Untested fn is process_ffg_deposits. Will add tests now.

src/utils/test_helpers.rs

@@ -1,13 +1,10 @@
 extern crate rand;
 
 use super::bls::Keypair;
-use self::rand::{ SeedableRng, XorShiftRng };
+use self::rand::thread_rng;
 
 // Returns a keypair for use in testing purposes.
 pub fn get_dangerous_test_keypair() -> Keypair {
-    let mut rng = XorShiftRng::from_seed([0xbc4f6d44, 
-                                         0xd62f276c, 
-                                         0xb963afd0, 
-                                         0x5455863d]);
+    let mut rng = thread_rng();
     Keypair::generate(&mut rng)
 }

src/utils/types.rs

@@ -4,6 +4,7 @@ use super::crystallized_state::CrystallizedState;
 use super::boolean_bitfield::BooleanBitfield;
 
 pub use super::blake2::Blake2s;
+pub use super::ethereum_types::U256;
 
 // TODO: presently the compiler accepts these two types
 // as interchangable. This is somewhat loose typing,