Add monitoring and some housekeeping

[seadanda]

Started on top of #154 and some of those commits remain to avoid force-pushing.

• Add just commands to build and run the monitoring backend
• Add instructions to use it on the deployed frontend at https://migration.paritytech.io/?backend_url=http://localhost:3000
• Add some cleaning commands
• Tidy up some stuff along the way

[ggwpez]

&& instead of #!/usr/bin/env bash + set -e for brevity or why?

[seadanda]

&& really mainly for staying in same dir, just runs each line of a recipe with working directory as the root. I.e. here cd changes directory from the root to ahm-monitor/backend, then the next line is run in the root:

test:
    mkdir tmp
    cd tmp
    touch test

you'd end up with the behaviour of touch ./test, rather than the expected touch ./tmp/test

You can fix it with a shebang so it runs it all in the same instance, but I slightly prefer this as the recipes are then consistent, rather than throwing a shebang into some recipes but not others. don't feel too strongly about it though, happy to change if you think it's better style

[ggwpez]

Yarn here vs npm above? will it cause issues?

[seadanda]

yarn is enforced in the overall package.json, I found a way round it (it's basically just for tests) but forgot to revert this line

[kianenigma]

yeah man, I would love this :)) the repo still generates so many things that should be git-ignored on each run.