WIP: Docker and AWS CloudFormation support

[Sjors]

Fixes #31, combining ideas from #34 and #35.

Currently just spins up bitcoind on an EC2 instance using Docker.

Based in part on https://github.com/NicolasDorier/lightning-charge-docker/blob/master/docker-compose.yml and https://github.com/ElementsProject/lightning-charge/blob/master/Dockerfile

TODO:

• testnet / mainnet dropdown
• Postgres container
• Rails container (with yarn)
• configure FROM_EMAIL, BUGS_TO
• configure PODCAST, PODCAST_TITLE, PODCAST_IMAGE, PODCAST_URL
• map Charge to /charge instead of using port 9112 (and remove port from security group)
• show Lightning node info (via Display node URI on checkout page ElementsProject/lightning-charge#38)
• configure SMTP params
• use Rails production environment
• run crons
• Wait for IBD before starting c-lightning
• update README

Later (followup PRs):

• wait for c-lightning to start before starting Charge
• show IBD status on Matreon landing page, disable login / signup until complete
• avoid using root
• https support
• backup command / instructions (private keys, channel and invoice metadata, pg database)
• upgrade support (depends on files having a permanent path and user), both host OS and containers need to be updated