Generate a dynamic livebook based on encoded params

[joshk]

This is an experiment towards making it easier to connect to a device using Livebook.

I could see this being its own app, but since its just one dynamic template I'd prefer to keep it here, at least to start with.

This uses a livebook. subdomain for the route, and the node and cookie for the script are base64 encoded in the url.

eg. https://livebook.nervescloud.com/eyJub2RlIjoibmVydmVzQDEwMC4xMDguMTA0Ljg4IiwiY29va2llIjoiOHQ2UU9JNjNiNk0yc1E3Tm5sdzdJSzBoZ294a2RubUFST21MWURuSGpSdyJ9/nerves.livemd

[lawik]

I am good with it but will let @nshoes and @jjcarstens weigh in :)

[joshk]

I think I'm going to pull this out and put it into its own app, at least for now :)