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

The problem was caused by the improper usage of
`delegate_ctrl` when creating the coreNLP process. For a long
time I was under the impression this flag was essential to allow child
processes to shutdown cleanly without leaving zombie threads, but the
result here in the context of the testsuite was that the coreNLP server
was receiving the first Ctrl^C, completely starving the Haskell RTS,
which wouldn't receive any and as a result our testsuite would be
running forever.

By default, we shouldn't run debug logs for phylo in production, let
alone some that runs within pure code.

Debug logs will hinder performance, and showing them on the production
server is not their place anyway.

This commit correctly propagates the correct `LogConfig` in all the
places where we were just defaulting to log everything, and this allows
us to silence debug logs in tests, unless we want them.

Furthermore, the env var we used to override (in some parts) the logging
level from `LOG_LEVEL`  to `GGTX_LOG_LEVEL`, to avoid the env var
`LOG_LEVEL` clashing with some other service.

This will eventually allow us to properly override the logging level in
the tests, silencing non interesting stuff.

This will allow us to find all the use site of this function, trying to
see if we can use only `withLogger` or correctly control the logging
verbosity via the `HasLogger` and `LogInitParams`.

Nix does it now.

Removed some dead code, most notably the `Partition` and `PartitionMathod`
types which were not in actual use anywhere.
Also renamed some function arguments from single-/double-letter identifiers
to actual words.

In the process, did some restructuring of the `bridgeness` function
and removed the `Bridgeness` type, whose purpose was not clear.
Removed a bit of dead code in the process.

This commit uses the latest version of `gargantext-graph`, now rebranded
`gargantext-graph-core`, which allowed us to drop unused dependencies
like `accelerate-arithmetic` & co.