Relax a bit moveChecks to account for shared nodes

Closes #455

See merge request !398

Before we were repeating the same code to initialise all the different
loggers. This commit introduces two stock loggers called `ioStdLogger`
and `monadicStdLogger` which can be reused many times.

It also allows the `GGTX_LOG_LEVEL` to take effect during `readConfig`,
so that the `startupInfo` would show up the correct information.

We can use it to implement the specific case for `serveWorkerAPI`, while
giving the user the ability to do things in the monad `m`, like
introduce specific logging.

Also, remove caddy from docker-compose.

This commit fixes a bug where a user member of a team (but NOT the owner
of such team) couldn't move nodes.

No need to copy .nix files. They are bound by CI anyways.

Also, graphviz and igraph are in separate nix files now.