Add support for metamask's privacy mode

[Powersource]

This article describes it pretty well https://medium.com/metamask/https-medium-com-metamask-breaking-change-injecting-web3-7722797916a8
it talks about it from the perspective of websites, but I think it applies to us too.

Doesn't seem like major changes are needed (hopefully just a few lines) but either way, we need to fix this before the deadline.

[Powersource]

Ok not as simple as I thought, the metamask developers might have forgotten to implement this for connections from other browser extensions. Thankfully the privacy option is opt-in for now. We should file an issue and hope it gets fixed before it turns opt-out.

[Powersource]

Submitted an issue here https://github.com/MetaMask/metamask-extension/issues/5950

[ErikBjare]

Also discussed here: https://github.com/MetaMask/metamask-extension-provider/issues/3

[ErikBjare]

Temporary workaround issue: #200

[Powersource]

Maybe better workaround https://github.com/MetaMask/metamask-extension/issues/5950#issuecomment-508540452