Add coverage events

[alaibe]

New strategy for code coverage:

It requires solidity with emit keyword for event (0.4.21 or higher)
Instead of using the trace from the vm, use events that we inject into the contract.

Change required if you deploy your contract manually, instead of doing:
MyContract.deploy(deployArgs).send(sendArgs) do: embark.deploy(MyContract, deployArgs, sendArgs)

Otherwise we cannot fetch the events associated to this contract

Pros:

• 100% accurate on line count
• Support library
• Support all cases

Cons:

• Consume more gas
• You cannot extend a function from an external contract that is pure or view until we find a solution for: Feature Request: findImports allow to return promise. ethereum/solc-js#313

Possible improvements:

• Do not emit event for function and branch, in theory the statement are enough, so gas consumption would be reduced

[jrainville]

I'd say we should get rid of the function and branch events, as they are pretty much duplicated because of the statements.
Also, why did you remove the coverage app?

[alaibe]

I'd say we should get rid of the function and branch events, as they are pretty much duplicated because of the statements.

See PR description, I will do it in a following PR, this is already quite complex and big.

[iurimatias]

@alaibe can you rebase please.