[Audit Milestone] No rootchain finality checks

[hamdiallam]

• Rather than explicit finality checks, we enforce ordering in the block number parameter passed into a submitBlock call. The blocks can also be batched, increasing the throughput of the chain.

• We ended up not following through allowing people to insert blocks in the case of a reorg. Enforcing ordering prevents gaps anyways. There is no way to submit block N if block N-1 is not posted.

• Fixed tests to reflect the above.

[coveralls]

Coverage decreased (-0.03%) to 91.693% when pulling 44e2116b1ecd0d2d069af0b2940551f71a854a76 on hamdi/submitblock-opt into 62a9462741fe6427fef4e51d97fb1976094cda74 on master.

[colin-axner]

Can you update docs reflecting these changes