Fix some MetaMask bugs

[nicholaspai]

• Signing messages is different on MetaMask than Truffle, so need to call deriveKeyPairFromSignatureMetamask (from Crypto.js) when commiting and revealing votes, now commit, reveal work well
• Reading past event logs (via web3.contract.getPastEvents) doesn't work all the time, notably it works sometimes for reading VoteRevealed events but has never worked for PriceResolved. These events are needed to retrieve rewards and show price resolution results, respectively. Therefore, I have added checks to detect if the user is using a metamask provider and to subsequently block certain functionality if so.
• I have added messaging to communicate to the user that metamask may not work for certain functionality
• I forked node-metamask and fixed a bug where it does not properly convert scientific notation into numbers, notably when calling web3.eth.getBalance() on an account with a lot of ETH (e.g. 10,000 ETH), it retrieves this result as "1e+22" instead of "10000....000" which causes downstream bignumber errors. I made a PR into the main node-metamask repo about this.

This is part of #901

Resolves #953

[mrice32]

@chrismaree could you take a first pass on this?

[chrismaree]

I went through this and ran it locally. All works as expected except for an issue which is unrelated to this PR. I created an issue #953 . Also a number of persistent event issues remain but this is documented in #901 specifically when going through a commit-reveal process