Use estimateGas for gasLimit instead of arbitrary value

[TimDaub]

Scope

• Currently when sending a transaction from a metaAccount, we simply take an arbitrary gasLimit value e.g. 200000
• Often these transactions use way less gas
• web3 implements a method on its Contract methods interface that is estimateGas
• This runs a gasLimit simulation locally and returns a gasLimit that fairly accurately predicts how much gas will actually be spent

Deliverables

• Identify all occurrences where gasLimits are set arbitrarily and replace them with estimateGas

Gains for the project

• Users have to spend less money on sending transactions

Roles

bounty gardener: @TimDaub / 10%
bounty worker: name / 75%
bounty reviewer: name / 15%

[riusricardo]

@TimDaub Before creating this bounties, you need to take into account some previous limitations that we encountered on this.

1. xDai returns a bad estimation if it doesn't has a lot of transactions on the previous blocks. Attempt to evaluate a gas price before relaying a call #105 #9795
2. Metamask didn't accept the getGasPrice call on its web3 API.
   This is why it remained hard-coded. However it should be good to take another look and try to fix it.