refactor codebase with urfave/cli

[tiero]

Overview

This PR starts the groundwork for #113 simplifying the codebase: the main takeway is that we do not need to load compose files and nodes' configuration files out of band (ie. installer script) but we ship them inside the compiled binary using the new embed package introduced in the standard library from Go 1.6

This does not introduce or makes any breaking changes that can be noticed by end users of any means

Notable changes

• To change datadir will be used an env var NIGIRI_DATADIR instead of a global flag, which introduces a chicken-egg problem, since in the init of the main.go we check/provision the resources automatically, without using an installer script.
• a flag --ci has been added which will allow to run in headless mode (ie. without Esplora frontend) useful in continuos integration pipelines.
• an update command has been added to pull new docker images from the Github Container Registry

TODOs

• add --ci flag to run in headless mode
• change datadir via NIGIRI_DATADIR
• add update command to pull down new images
• reintroduces testing suite
• Update Makefile
• Update scripts
• update GH actions

[tiero]

Still not satisfied about hot properly test it. Provably the best way should be an e2e building the binary and run it from go code.

[altafan]

This refactor was soooo much needed! thanks for the effort.

I have a question: is this intended to let one start multiple nigiris up on the same machine? If so the exposed ports of the services of the compose file must not be hardcoded.

[tiero]

is this intended to let one start multiple nigiris up on the same machine

At that point someone can use different data directory and manually tweak the compose that is moved there.

# start first
nigiri start --liquid
# only provision datadir
nigiri --datadir=mydata version
# tweak compose in ./mydata
# nigiri --datadir=mydata start --liquid