Set up cargo-deny (Rust) and license-checker-webpack-plugin (Node)

[Keavon]

We need to add license compatibility checkers to our CI to ensure no copyleft or Apache2-incompatible licenses are ever merged into the project, even as transient dependencies.

For Rust dependencies from crates.io, we should use Embark's cargo-deny.

For Node dependencies from npm, I found license-checker looks reasonably popular, but popular alternatives would also be fine. (Edit: we ended up using Microsoft's license-checker-webpack-plugin)

• Rust (cargo-deny)
• Node.js (license-checker-webpack-plugin)

[Keavon]

Hey @bjorn3, I know you helped out with some infrastructure-related stuff in the past and this is also infrastructure-related. If you're not too busy and if this sounds interesting to you, do you think you'd be up for taking on this (presumably small) task? If not, no worries, I just thought I'd ask.

[bjorn3]

Opened #358 for cargo-deny. I think someone else will need to do the node side of this issue.