[Audit Milestone] Exits

[hamdiallam]

1.) Added transaction position to the exit structure and appropriate events

• Position = [blockNum, txIndex, outputIndex, depositNonce]

2.) Removed getter functions from contract. Public variables can be queried directly

3.) Tests reflect the above

[coveralls]

Coverage decreased (-0.2%) to 91.72% when pulling 9d793777471707c9ceba56c06cdc684aa5127ab2 on hamdi/exit-position into ab4fd0ed780c5828ca815946922ba3b05c1e9de4 on master.