Address cs audit 5.5

[cwang25]

• Can be merged after refactor, should be easy to rebase this.
• Now treat "" as empty code, codeExists will return false if code is ""

Open question:
Mentioned in #quark-eng channel

Question on ChainSecurity [5.5] Correctness feedback. 
So it's saying that sending a eth to a empty address will cause our codeJar.codeExists() return true. Cuz having eth in it the codehash will be equal to keccak256(""). 
Was thinking codeExists should also check on the code.length > 0 if the code exsits there. "
But in testCodeJarInputVariety it looks like we treat deploying "" as a valid code. 

So was curious if we should treat all empty code (includeing "") as not exists?  (It's a bit tricky to say to check on eth balance if detect codeHash == keccak256("") cuz that's the same as deploy a "" code and send eth to it 🤔 )