meta(license): switch licensing scheme for the project

[zkat]

Fixes: #18

After speaking with @ceejbot and @chrisdickinson, we agreed to put up a proposal for licensing based on the Parity License by @kemitchell.

This PR has the following effects:

1. All JavaScript source code, under /dstopic, will be licensed under Apache from now on.
2. The rest of the code, that is, all the Rust stuff, will be licensed under Parity for changes done by the core team.
3. Third-party PRs will have their changes licensed under Apache 2.0 for ease of relicensing.
4. Proprietary-use licenses will be made available either through subscriptions on OpenCollective, or by directly purchasing a license by emailing us.
5. Proprietary-use licenses will be immediately denied to any organization working with ICE or the military industrial complex.

[chrisdickinson]

IANAL, but this LGTM.