Demo uses local React, jQuery; dependencies update

Swarm has an objective of making offline-ready apps. Then, it is absolutely
outrageous that the demo fetches libs from CDNs and thus offline
development is not possible. Changed it to use local copies.
PostMessageStream does a handshake now

Iframe load process creates some unexpected races. Namely, the parent
frame may not be initialized at the time the child attempts a
postMessage connection. Thus, the initial message goes nowhere.
Added PostMessageStream handshake, retries and message buffering.